The future of the force: Better think twice before cutting lots of heavy ground units

Here is an excerpt from an e-book, The Wounded Giant: America’s Armed Forces in an Age of Austerity, to be published next week by Penguin Press.

By Michael O’Hanlon
Best Defense guest commentator

During the Vietnam War, the United States Army’s active-duty forces were almost a million and a half soldiers strong. In World War II, the number had approached six million (not counting the Army Air Force or other services). Under Ronald Reagan, the figure was more like 800,000. After reducing that strength when the Cold War ended to less than half a million, and after considering Donald Rumsfeld’s ideas in early 2001 to cut even more, the nation built up its standing Army by almost 100,000 troops over the last decade, while modestly increasing the size of the Marine Corps from about 170,000 to 200,000 active-duty Marines as well. We are now on a downward slope again. But how low can we go?

It is easy to see the pros and cons of deeper cutbacks. On the favorable side, we are a nation tired of war, and especially tired of long counterinsurgency missions in distant Asian lands — not for the first time in our history. In addition, we have oceans to protect us from most potential adversaries, and high-technology weapons to try to keep the peace without putting U.S. troops on the ground in distant lands. On the other hand, in Iraq and Afghanistan over the last decade, we have relearned the lesson that if you want to enhance the stability of a faraway land, you cannot do it with the “shock and awe” of air and missile strikes alone. In addition, if you go in too small, you may only worsen the situation and have to salvage it with larger forces later. Moreover, the size of armies needed to help stabilize such places is partly a function of the size of their populations, not just the quality of our technology or our troops on a person-by-person basis. In a world with more than six billion people, hundreds of millions of whom are still living in turbulent places that could threaten U.S. interests, it is not clear that the American Army can keep getting smaller.

And even if we try simply to avoid manpower-intensive war in the future, we may just fail. We have tried that approach before, deciding that as a nation we were simply done with certain forms of combat. But then we have usually wound up being forced by the course of history to re-learn old lessons and re-create old capabilities when our crystal balls proved to be cloudy, and our predictions about the nature of future combat proved wrong. The stakes involved in faraway lands in the age of transnational terrorism and nuclear weapons are too high for us to blithely assume that we’ve seen the last of complex ground missions in distant lands just because we don’t happen to like them.

The U.S. military today is indeed the second largest military in the world, after China’s. But it is only modestly larger than those of North Korea, India, and Russia. The size of its active-duty Army also only modestly surpasses that of South Korea and Turkey, among others. So as we begin the debate about its future size, we are not exactly beginning with a huge force as a starting point.

Nevertheless, the U.S. military probably can become smaller as the wars in Iraq and Afghanistan wind down. We should not rush into this, and we should not adopt the attitude some advocate that America’s main overseas capabilities be reduced principally to Air Force and Navy capabilities. The latter services are formidable and essential. But “standoff” warfare featuring long-range strikes from planes and ships cannot address many of the world’s key security challenges today — and possible scenarios in places like Korea and South Asia, discussed further below, that could in fact imperil American security. In the 1990s, advocates of military revolution often argued for such an approach to war, but the subsequent decade proved that for all our progress in sensors and munitions and other military capabilities, we still need forces on the ground to deal with complex insurgencies and other threats.

An emphasis on standoff warfare is sometimes also described as a strategy of “offshore balancing” by which the distant United States steps in with limited amounts of power to shape overseas events, particularly in Eurasia, rather than getting involved directly with its own soldiers and Marines. But offshore balancing is too clever by half. In fact, overseas developments are not so easily nudged in favorable directions; proponents of this approach actually overstate American power. It also suggests a lack of real American commitment. That can embolden adversaries and worry friends to the point where, among other things, they may feel obliged to build up their own nuclear arsenals — as the likes of South Korea, Japan, Taiwan, Turkey, Egypt, and Saudi Arabia might well do absent strong security ties with America.

All that said, we will have to streamline in the years ahead. This is not really for any lack of manpower to people a larger Army and Marine Corps. We have nearly five million young people reaching eighteen every year, and need to recruit only about 200,000 at present for the current military. Although many of the remaining 4.8 million do not qualify for today’s force due to their lack of fitness, educational attainment, or other characteristics, ways could be found to make more of them eligible — such as my friend Marshall Rose’s idea of premilitary fitness camps that could whip out-of-shape young men and women into shape with incentives for positive completion. At present, however, and certainly for as long as the U.S. economy remains weak, availability of manpower will not be our limiting factor. Rather, it is that the expense of having people in uniform has become so great that we must not have more troopers than we need.

As such, once the wars wind down, we should reverse the recent increases in the active forces of the U.S. Army and Marine Corps and return to Clinton and early Bush levels. That would mean roughly 15 percent cuts, relative to current combat force structure — roughly twice the cut currently planned by the services. There was in fact a reasonable amount of bipartisan consensus on those earlier force levels, with defense secretaries Aspin, Perry, Cohen, and Rumsfeld all supporting them over a ten-year period. These reductions in ground forces would not quite achieve 15 percent reductions in costs, as certain nonlinearities exist. New weapons must still be developed regardless of how many will be purchased; weapons unit costs tend to go up when fewer are purchased; some support activities like intelligence do not decline automatically when force structure is cut. But savings would be 10 to 12 percent in the ground forces, or $15 billion to $18 billion in annual spending. Commensurately, Air Force tactical combat forces might be cut 10 percent.

To give a sense of the respective facts and figures, today’s U.S. Army has about 550,000 active-duty soldiers. In addition, as of early 2011 data, another 110,000 reservists had been temporarily activated — nearly 80,000 from the National Guard and just over 30,000 from the Army Reserve. The U.S. Marine Corps is about 200,000 strong, with another 5,000 Marine reservists temporarily activated. By contrast, the active Army of 2000 was 472,000 strong and the Marine Corps numbered 170,000. Excluding activated reservists, therefore, making 15 percent personnel cuts would reduce current levels approximately to those of a decade ago.

Today’s Army likes to organize its forces and measure its strength more in terms of brigades than the old standard of divisions; there are usually now four brigades to a division, and the former have been turned into units that are independently deployable and operable in the field. Today’s ground forces include forty-five brigade combat teams in the active Army as well as twenty-eight in the National Guard. The Army also has thirteen combat aviation brigades in the active force and eight in the reserve component. The Marines, organized somewhat differently and using different terminology to describe their main formations, have eleven infantry regiments as well as four artillery regiments. Roughly speaking, a Marine Corps regiment is comparable in size and capability to an Army brigade.

Throughout the 1990s, U.S. ground forces were sized and shaped primarily to maintain a two-war capability. The wars were assumed to begin in fairly rapid succession (though not exactly simultaneously), and then overlap, lasting several months to perhaps a year or two. Three separate administrations — Bush 41, Clinton 42, and Bush 43, and a total of five defense secretaries — Cheney, Aspin, Perry, Cohen, Rumsfeld — endorsed some variant of it. They formalized the logic in the first Bush administration’s 1992 “Base Force” concept, the Clinton administration’s 1993 “Bottom-Up Review” followed four years later by the first Quadrennial Defense Review, and then Secretary Rumsfeld’s own 2001 QDR. These reviews all gave considerable attention to both Iraq and North Korea as plausible adversaries. More generally, though, they postulated that the United States could not predict all future enemies or conflicts, and that there was a strong deterrent logic in being able to handle more than one problem at a time. Otherwise, if engaged in a single war in one place, the United States could be vulnerable to opportunistic adversaries elsewhere. With Saddam Hussein gone, this deterrent logic can be adjusted, a point to which we return below.

In these debates in the dozen years following the Cold War and Desert Storm, most considered actual combat in two places at once unlikely. Few predicted prolonged wars in two places at once. Yet we got exactly that in Iraq and Afghanistan over the last ten years. Of course, many disagreed with the decision to go to war in Iraq in particular. But the basic fact that conflict is unpredictable — that, to quote the old aphorism, “You may not have an interest in war but war may have an interest in you” — endures.

The Obama administration appears to agree; as its 2010 Quadrennial Defense Review Report states, after successfully concluding current wars, “In the mid- to long term, U.S. military forces must plan and prepare to prevail in a broad range of operations that may occur in multiple theaters in overlapping time frames. This includes maintaining the ability to prevail against two capable nation-state aggressors. . . . “The Obama QDR is actually somewhat more demanding than the military requirements that guided American planners between 1991 and 2001. It adds a stabilization mission and smaller operations on top of the two-war requirement, though it may be overestimating the capacities of its force structure in doing so.

In my judgment, though, a two-land-war capability is no longer appropriate for the age of austerity. The “one war plus several missions” framework proposed here for sizing combat forces — “one plus two” for short, if the two is understood as two relatively significant efforts — is designed to be a prudent but still modest way to ensure this type of American global role. It is prudent because it provides some additional capability if and when the nation again engages in a major conflict, and because it provides a bit of a combat cushion should that war go less well than initially hoped. It is modest, verging on minimalist, however, because it assumes only one such conflict at a time (despite the experience of the last decade) and because it does not envision major ground wars against the world’s major overseas powers on their territories.

More specifically, if there ever was conflict pitting the United States against China or Iran, for example, it is reasonable to assume that the fighting would be in maritime and littoral regions. That is because the most plausible threat that China would pose is to Taiwan, or perhaps to neighboring states over disputed sea and seabed resources, and because the most plausible crisis involving Iran would relate either to its nuclear program or to its machinations in and about the Persian Gulf waterways. It is reasonable for the United States to have the capability for just one ground war at a time as long as it can respond in other ways to other possibly simultaneous and overlapping challenges abroad.

Having such a single major ground-war war capability is somewhat risky, underscoring the risks of even deeper defense cuts than I am outlining here. But it is hardly radical or unprecedented. During the Cold War, American defense posture varied between periods of major ambition — as with the “2½ war” framework of the 1960s that envisioned simultaneous conflicts against the Soviet Union (probably in Europe), China in East Asia, and some smaller foe elsewhere — and somewhat more realistic approaches, as under Nixon, which dropped the requirement to 1½ wars. Nixon’s “1 war” would have been conflict in Europe against the Warsaw Pact, a threat that is now gone. His regional war capability, or his “½ war” posture, was therefore similar to what I am proposing here. Nor does this proposal lead to a dramatically smaller ground force. Having the capacity to wage one major regional war with some added degree of insurance should things go wrong, while sustaining two to three protracted if smaller deployments, is only modestly less demanding than fighting two regional wars at once. Unfortunately, today’s world does not allow a prudent decision to go to an even less demanding strategic construct or an even smaller force.

This one-war response capability needs to be responsive and highly effective to compensate for its modest size. That fact has implications in areas like strategic transport, discussed further in the next chapter. It also has implications for the National Guard and Reserves. They remain indispensable parts of the total force. They have done well in Iraq and Afghanistan, and merit substantial support in the years ahead — better than they have often received in our nation’s past. But they are not able to carry out prompt deployments to crises or conflicts the way that current American security commitments and current deterrence strategy require. As such, we should not move to a “citizens’ army” that depends primarily on reservists for the nation’s defense.

Translating this new strategy — one war, plus several smaller missions — into force planning should allow for roughly 15 percent cutbacks. Army active-duty brigade combat teams might number about thirty-eight, with the National Guard adding twenty-four more. Combat aviation units might decline to eleven and seven brigades in the active and National Guard forces, respectively. The Marines would give up perhaps two units, resulting in ten infantry and three artillery regiments respectively in their active forces, while keeping their three divisions and three associated Marine Expeditionary Forces. This force would be enough to sustain about twenty combat brigade teams overseas indefinitely, and to surge twenty-five to thirty if need be. If the United States found itself in a major operation, it could and should begin to reverse these cuts immediately, building up larger active ground forces as a hedge against the possibility that the new operation (or additional ones) could prove longer or harder than first anticipated. But that would take some time, roughly two to five years to make a meaningful difference, and as such the peacetime cuts should not go too far.

The above deployment math is based on the principle that active forces should have roughly twice as much time at home as on deployment and that reservists should have five times as much time at home as abroad — even in times of war. That would be enough for the main invasion phase of the kinds of wars assumed throughout 1990s defense planning and the invasion, occupation, and stabilization of Iraq actually carried out in 2003; force packages ranging from fifteen to twenty brigades were generally assumed or used for these missions. So the smaller force could sustain an Iraq-like mission for months or even years while also doing smaller tasks elsewhere.

This capacity falls short of the twenty-two brigades deployed in 2007-8 just to Iraq and Afghanistan, to say nothing of Kosovo or Korea, where additional brigade-sized forces were also present in that time period. If multiple long crises or conflicts occurred in the future, we would have to ratchet force strength back up. Thankfully, the Army and Marine Corps of the last ten years proved they can do this. They added that 15 percent in new capability within about half a decade without any reduction in the excellence of individual units.

Somewhat greater savings — $5 billion to $8 billion more per year — could be realized if the same capability was retained but more of it was located within the Army National Guard. Rather than downsize from forty-five active brigade combat teams and twenty-eight Guard teams to respective figures of thirty-eight and twenty-four, as recommended, one might reduce the active brigades down to just twenty-eight in number for example. The active-duty Army would wind up totaling fewer than 400,000 soldiers with this proposal. The overall U.S. military might compensate by adding not just ten but twenty National Guard brigade combat teams to its force structure, for a total of forty-four. That would keep unchanged the total Army ability to carry out a long-term deployment at acceptable deployment rates for reservists. (In other words, it would add enough additional Guard brigades that their numbers would compensate for the fact that they couldn’t be used as often as active units.) This would amount to a major shift in the character of the American Army and would place huge faith in the reserve component. Arguably, the reserve component has proven in recent years that it is up to the task. With twenty-eight active brigades, the Army would still have enough capability to conduct two or three missions while having perhaps fifteen to twenty active-duty brigades ready for quick deployment to a war. However, if a war did begin, the Army would need to move very fast to mobilize a dozen or more Guard brigades to allow them the time needed to train properly so that they could replace the initial response force within a year or so if the operation was not quickly concluded. I am uncomfortable with this degree of reliance on the reserves given the time pressures involved, but it is worth acknowledging that the option does exist.

Some might question whether we even still need a one-war capability. Alas, it is not hard to imagine plausible scenarios. Even if each specific case is unlikely, a number of scenarios cannot be ruled out. What if insurgency in Pakistan began to threaten that country’s nuclear arsenal, and the Pakistani army concluded that it needed our help in stabilizing their country? Far-fetched at present, to be sure — but so was the idea of war in Afghanistan if you had asked almost any American strategist in 1995 or 2000. Or perhaps, after another Indo-Pakistani war that reached the nuclear threshold, the international community might be asked to lead a stabilization and trustee mission in Kashmir following a ceasefire — not an appealing prospect to anyone at present, but hard to rule out if a nuclear exchange put the subcontinent on the brink of complete disaster. What if Yemen’s turmoil allowed al-Qaeda to set up a major sanctuary there like it did in Afghanistan fifteen years ago? What if North Korea began to implode and both South Korea and the United States felt the need to restore order before the former’s estimated nuclear arsenal of perhaps eight bombs wound up in the wrong hands?

Consider the Korea case in more detail. This would not necessarily be a classic war; it could result, for example, from an internal coup or schism within North Korea that destabilized that country and put the security of its nuclear weapons at risk. It could result somewhat inadvertently, from an exchange of gunfire on land or sea that escalated into North Korean long-range artillery and missile attacks on South Korea’s close-by capital of Seoul. If the North went down this path, something that its brazen 2010 sinking of the South Korean navy ship Cheonan and subsequent attacks on a remote South Korean island that together killed about fifty South Koreans suggest not to be impossible, war might occur out of an escalatory dynamic the two sides lost control over. Certainly the way in which North Korea remains a hypermilitarized state, devoting by far the largest fraction of its national wealth to its military of any country on Earth, while accepting that many of its people wallow in poverty or even starve, should make one worry somewhat. Perhaps Pyongyang might be inclined to try to use that military — in an attempt at brinkmanship or extortion that was foolish to be sure, but that could still prove quite dangerous. It is largely because of such possibilities that the United States should not abandon its South Korean ally, even though that nation is now far stronger than it used to be and stronger than North Korea. The risks of deterrence failure would be too great, given Pyongyang’s proclivities to attempt brinkmanship and intimidation. If we did break the alliance, hypothetically speaking, another likely outcome would be South Korean development of a nuclear arsenal, with further erosion of global nonproliferation standards as a result. It is not a risk worth taking now.

It is also possible that if North Korea greatly accelerated its production of nuclear bombs, of which it is believed to now have about eight, or seemed on the verge of selling nuclear materials to a terrorist group, the United States and South Korea might decide to preempt with a limited strike against DPRK nuclear facilities. North Korea might then respond in dramatic fashion. Such a war cannot be ruled out.

Given trends in the military balance over the years, the allies would surely defeat North Korea in such a war and then occupy its country and change its government. North Korea’s weaponry is more obsolescent than ever, it faces major fuel and spare parts shortages in training and preparing its forces, and its personnel are undernourished and otherwise underprepared. Yet horrible things could still happen en route to allied victory. The nature of the terrain in Korea means that much of the battle would ultimately be infantry combat. Whatever its other problems, North Korea’s rifles still shoot and its soldiers are still indoctrinated with the notion that they must defend their homeland at all costs. North Korea has built up fortifications near the DMZ for half a century that are formidable and could make the task of extricating its forces difficult and bloody. North Korea also has among the world’s largest artillery concentrations, and could conduct intense shelling of Seoul in any war without having to move most of its forces at all.

Even nuclear attacks by the North against South Korea, Japan, or American assets could not be dismissed. Sure, outright annihilation of Seoul or Tokyo would make little sense, as the United States could and almost surely would respond in kind, and allied forces would track down the perpetrators of such a heinous crime to the ends of the Earth. Any North Korean nuclear attack on a major allied city would mean certain ultimate overthrow of the offending regime, and almost surely death (or at least lifetime imprisonment) for its leaders once they were found. But the point about nuclear war is that it wouldn’t necessarily start that way, and therefore it is not so easy to dismiss out of hand. Perhaps North Korea would try to use one nuclear bomb, out of its probable arsenal of eight or so, against a remote airbase or troop concentration. This could weaken allied defenses in a key sector, while also signaling the North’s willingness to escalate further if necessary. It would be a hugely risky move, but not totally inconceivable given previous North Korean actions.

Possible Chinese intervention would have to be guarded against too. To be sure, in the event of another Korean war, Beijing is not going to be eager to come to the military defense of the most fanatical military dictatorship left on the planet. But it also has treaty obligations with the North that may complicate its calculations. And it is going to be worried about any possibility of American encroachment into North Korean lands near its borders. For all these reasons, a Korean war could have broader regional implications — and pose huge threats to great-power peace. This worry requires that Washington and Seoul maintain close consultations with Beijing in any future crisis or conflict. But it also suggests that U.S. and South Korean forces would want to have the capability to win any war against the North quickly and decisively. That would reduce the odds that China would decide to establish a buffer zone in an anarchic North Korea with its own forces in a way that could bring Chinese and allied soldiers into close and tense proximity again. If China insisted on creating such a buffer zone temporarily, by the way, it would be preferable to allow the PRC to do so rather than fight it to prevent such a possibility, in my judgment — to avoid turning this conflict scenario into a possible repeat performance of the first Korean War.

So what does this all add up to, in terms of American force requirements for a possible future Korean contingency? Again, let me underscore my hope that such a horrible war will never occur, and indeed my prediction that it will not. But hope is not a strategy, as Colin Powell liked to say, and in addition often the best way to preserve the peace when dealing with a state like North Korea is to be absolutely clear in one’s own resolve and absolutely prepared in military terms. To accomplish this, necessary U.S. forces would have to be quite substantial. They might focus principally on air and naval capabilities, given South Korea’s large and improved army. But they should also involve American ground forces, since a speedy victory would be of the essence, and since as noted the fighting could be quite difficult and manpower intensive. While South Korea is very capable, and has a better military than does North Korea, it would be important to win fast to limit damage to Seoul and to seal off North Korea’s borders in order to prevent the smuggling out of nuclear materials.

American ground forces would also be important because American mobile assets (such as the 101st air assault division and Marine amphibious forces) provide capabilities that South Korea does not itself possess in comparable numbers. Perhaps fifteen to twenty brigade-sized forces and eight to ten fighter wings, as well as three to four carrier battle groups, would be employed, as all previous defense reviews of the post-Cold War era have concluded. American forces might not be needed long in any occupation, given South Korea’s large capabilities, but could be crucial for a few months.

U.S. Forces that were 15 percent smaller than today’s would admittedly be hard-pressed in certain other scenarios. They probably could not stabilize a country like Iran, for example. In the unlikely but not impossible event that, due to dramatic Iranian escalation in use of terrorism or weapons of mass destruction, we felt the need to intervene on the ground in that country, a smaller U.S. Army and Marine Corps would be a disadvantage. There is no denying it.

Even in this case, however, we would not lack options. We would retain the ability, even without allied help on the ground, to overthrow a regime such as that in Tehran that carried out a heinous act of aggression or terror against American interests in the future. Such a deterrent could also be useful against any other powerful extremist government with ties to terrorists and nuclear ambitions or capabilities, should it someday take power in another country (above and beyond a current case like North Korea). The force would not be enough to occupy and stabilize a country like Iran thereafter. And leaving it in chaos would hardly be an ideal outcome. But this capability could nonetheless be a meaningful deterrent against Iranian extremism, as we could defeat and largely destroy the Revolutionary Guard and Qods Forces that keep the current extremists in power if it ever became absolutely necessary. That translates into a meaningful deterrent capability — which is of course what we are after, since dissuading the extremists in Tehran from worse behavior in the first place is our real goal. To the extent the international community as a whole then saw the reestablishment of order in Iran as important, it could if desired help provide ground forces in a subsequent coalition to stabilize the place — a job that could require half a million total troops. (Thus, even today’s American ground forces would in fact be inadequate to the job of stabilizing Iran, which with 80 million people is three times as populous as either Iraq or Afghanistan.)

For missions like helping stabilize a large collapsing state, perhaps Pakistan or Nigeria, smaller U.S. ground forces could well prove sufficient as part of a coalition. That is, they might suffice if part of the security forces of the state at issue remained intact, or if a broader international coalition of states contributed to the operation.

Consider one of these — the Pakistan scenario — in more detail. Such a scenario is extremely unlikely; for all its challenges, Pakistan does not appear on the verge of collapse. It is also important to underscore, especially in this period of fraught U.S.-Pakistan relations, that any international effort to help Pakistan restore order to its own territory could only be carried out with the full acquiescence, and at the invitation of, its government. That is because there is no scenario I can imagine in which Pakistan’s army would entirely melt away, meaning that it would be a force we would have to reckon with and in fact want to work with regardless of circumstances. It is also because the country is so huge that the task would be unthinkably demanding, even with today’s military, if the U.S. and international roles were not primarily in support of indigenous efforts. Even independent American writers like me can worry Pakistanis with discussion of such scenarios, and the May 2011 killing of bin Laden only exacerbates the Pakistani sensitivities to any discussion of scenarios that would infringe upon their sovereignty. But we cannot avoid the issue.

Of all the military scenarios that undoubtedly would involve U.S. vital interests, a collapsed Pakistan ranks very high on the list. The combination of Islamic extremists and nuclear weapons in that country is extremely worrisome. Were parts of Pakistan’s nuclear arsenal ever to fall into the wrong hands, al-Qaeda could conceivably gain access to a nuclear device with terrifying possible results. The Pakistan collapse scenario appears somewhat unlikely given the country’s traditionally moderate officer corps; however, some parts of its military as well as the intelligence services, which created the Taliban and have condoned if not abetted Islamic extremists in Kashmir, are becoming less moderate and less dependable. The country as a whole is sufficiently infiltrated by fundamentalist groups — as the attempted assassinations against President Pervez Musharraf in earlier days, the killing of Benazir Bhutto in 2007, and other evidence make clear — that this terrifying scenario should not be dismissed.

Were Pakistan to collapse, it is unclear what the United States and like-minded states would or should do. As with North Korea, it is highly unlikely that “surgical strikes” to destroy the nuclear weapons could be conducted before extremists could make a grab at them. The United States probably would not know their location — at a minimum, scores of sites controlled by special forces or elite army units would be presumed candidates — and no Pakistani government would likely help external forces with targeting information. The chances of learning the locations would probably be greater than in the North Korean case, given the greater openness of Pakistani society and its ties with the outside world; but U.S.-Pakistani military cooperation, cut off for a decade in the 1990s, is still quite modest, and the likelihood that Washington would be provided such information or otherwise obtain it should be considered small.

If a surgical strike, series of surgical strikes, or commando-style raids were not possible, the only option would be to try to restore order before the weapons could be taken by extremists and transferred to terrorists. The United States and other outside powers might, for example, respond to a request by the Pakistani government to help restore order. Given the embarrassment associated with requesting such outside help, the Pakistani government might delay asking until quite late, thus complicating an already challenging operation. If the international community could act fast enough, it might help defeat an insurrection. Another option would be to protect Pakistan’s borders, therefore making it harder to sneak nuclear weapons out of the country, while providing only technical support to the Pakistani armed forces as they tried to quell the insurrection. Given the enormous stakes, the United States would literally have to do anything it could to prevent nuclear weapons from getting into the wrong hands.

Should stabilization efforts be required, the undertaking could be breathtaking in scale. Pakistan is a very large country: its population is over 175 million, or six times Iraq’s; its land area is roughly twice that of Iraq; its perimeter is about 50 percent longer in total. Stabilizing a country of this size could easily require several times as many troops as the Iraq mission, and a figure of up to one million is plausible. However, that assumes complete collapse.

Presumably, any chaos within Pakistan would be localized and limited, at least at first. Some fraction of Pakistan’s security forces would remain intact, able and willing to help defend their country. Pakistan’s military includes more than half a million soldiers, almost 100,000 uniformed air force and navy personnel, another half million reservists, and almost 300,000 gendarmes and Interior Ministry troops. Nevertheless, if some substantial fraction broke off from the military — say, a quarter to a third — and was assisted by extremist militias, it is quite possible the international community would need to deploy 100,000 to 200,000 troops to restore order quickly. The U.S. requirement could be as high as 50,000 to 100,000 ground forces. The smaller force discussed here could handle that.

As noted, another quite worrisome South Asia scenario could involve another Indo-Pakistani crisis leading to war between the two nuclear-armed states over Kashmir, with the potential to destabilize Pakistan in the process. This could result, for example, from a more extremist leader coming to power in Pakistan. Imagine the dangers associated with a country of nearly 200 million with the world’s fastest-growing nuclear arsenal, hatred of India as well as America, and claims on land currently controlled by India. I do not suggest that we should create the option of directly attacking such a hypothetical future Pakistan. That said, some scenarios could get pretty hairy — for example, if that future government in Islamabad had ties to extremists and thought about supporting them militarily. Certainly if such a future government was involved directly or indirectly in attacking us, we would need options to respond. These should include the possibility of a naval blockade and scale up from there as necessary, along the lines of the capabilities discussed above regarding Iran.

Even more plausibly, it is easy to see how such an extremist state could take South Asia to the brink of nuclear war by provoking conflict with India. Were that to happen, and perhaps a nuke or two even popped off above an airbase or other such military facility, the world could be faced with the specter of all-out nuclear war in the most densely populated part of the planet. While hostilities continued, even if it would probably avoid taking sides on the ground, the United States might want the option to help India protect itself from missile strikes by Pakistan. It is even possible that the United States might, depending on how the conflict began, consider trying to shoot down any missile launched from either side at the other, given the huge human and strategic perils associated with nuclear-armed missiles striking the great cities of South Asia. The United States might or might not be able to deploy enough missile defense capabilities to South Asia to make a meaningful difference in any such conflict. But certainly if it had the capacity, one can imagine that it might be prudent to employ it in certain circumstances.

It is also imaginable that, if such a war began and international negotiators were trying to figure out how to end it, an international force could be invited to help stabilize the situation for a number of years. India in particular would be adamantly against this idea today, but things could change if war broke out and such a force seemed the only way to reverse the momentum toward all-out nuclear war in South Asia. American forces would quite likely need to play a key role, as others do not have the capacity or political confidence to handle the mission on their own.

With forty-nine brigade equivalents in its active Army and Marine Corps forces, and another twenty-four Army National Guard brigades, the United States could handle a combination of challenges reasonably well. Suppose for example that in the year 2015, it had one brigade in a stabilization mission in Yemen, two brigades still in Afghanistan, and two brigades as part of a multinational peace operation in Kashmir. Suppose then that another war in Korea breaks out, requiring a peak of twenty U.S. combat brigades for the first three months, after which fifteen are needed for another year or more. That is within the capacity of the smaller force — though just barely. Specifically, after the initial surge to Korea, the United States would by these assumptions settle back into a set of missions that required twenty brigade equivalents in all for some period of a year or more. The ground forces designed here would be up to the task.

Of course, with different assumptions it would be possible to generate different force requirements, making my recommended force look too small or alternatively bigger than necessary. But the demands assumed above are not capricious. They are based on real war plans for Korea, and very plausible assumptions about two to three possible missions elsewhere. And they do not take the U.S. military too far below levels that have recently been necessary for Iraq and Afghanistan, given that recent history should remind us of any overconfidence about predicting the end of the era of major ground operations abroad.

One final important point demands attention in this analysis of scenarios around the world: what is the role of U.S. allies in each of them? The fact that America has so many allies is extremely important — it signals that most other major powers around the world are at least loosely aligned with America on major strategic matters. They may not choose to be with us on every mission, as the Iraq experience proves. But when America is directly threatened, as in 9/11, the Western alliance system is rather extraordinary. This has been evidenced in Afghanistan, where through thick and thin, even at the ten-year mark of the war, the coalition still includes combat forces from some forty-eight countries.

Yet how much help do these allies tend to provide? Here the answer is, and will remain, more nuanced. The other forty-seven nations in Afghanistan have, in 2011, collectively provided less than one third of all foreign forces; the United States by itself provided more than two thirds. Still, more than forty thousand forces is nothing to trivialize.

The allies have taken the lead in Libya in 2011. But this may be the exception that proves the rule — the mission that they led was a very limited air campaign in a nearby country. The French also helped depose a brutal dictator in Ivory Coast in 2011, and some European and Asian allies as well as other nations continue to slog away in peace operations in places such as Congo and Lebanon. The Australians tend to be dependable partners, Canada did a great deal in Afghanistan and took heavy losses before finally pulling out its combat forces in 2011, and over in Asia, the Japanese are also showing some greater assertiveness as their concerns about China’s rise lead to more muscular naval operations by Tokyo.

For future American strategy, however, we should keep our expectations in check. Overall, the allies are not stepping up their game to new levels. Any hope that the election of Barack Obama with his more inclusive and multilateral style of leadership would lead them to do so are proving generally unwarranted. NATO defense spending is slipping downward, from a starting point that was not very impressive to begin with. The allies were collectively more capable in the 1990s, when they contributed most of the ground troops that NATO deployed to the Balkans, than they are now.

The fraction of the NATO allies’ GDP spent on their armed forces has declined to about 1.7 percent as of 2009, well under half the U.S. figure. That is a reduction from NATO’s earlier figure of 2.2 percent in 2000 and about 2.5 percent in 1990. Secretary Gates accordingly warned of the possibility of a two-tier alliance before leaving office in 2011. Yet NATO is still an excellent insurance policy should trouble loom in the future with China, Russia, or another power. As a time-tested community of democracies sharing common values and historical experiences, the alliance offers America a very useful anchor in sometimes unstable Eurasian waters.

The bottom line is this: When allies feel directly threatened, as Japan and South Korea sometimes do now, they will pony up at least to a degree. South Korea in particular can be counted on to provide many air and naval forces, and most of the needed ground forces, for any major operation on the peninsula in the future. (South Korea is less enthusiastic about being pulled into an anti-China coalition, and Washington needs to watch not only the substance but even the tone of its comments on this subject.) Taiwan would surely do what it could to help fend off a possible Chinese attack, not leaving the whole job to the American military in the event that terrible scenario someday unfolds, though it is probably underspending on its military (see below for more on this). Many if not most NATO forces will be careful in drawing down troops from Afghanistan, making cuts roughly in proportion to those of the United States over the next two to three years.

In the Persian Gulf, both Saudi Arabia and the United Arab Emirates have impressive air forces, with at least one hundred top-of-the-line aircraft each. Both countries could certainly help provide patrols over their own airspace as defensive measures in a future conflict. If they had already been directly attacked by Iran, they might also be willing to carry out counterstrikes against Iranian land or sea targets. But again there are limits. Neither country trains that intensively on a frequent basis with the United States to the point where combined combat operations in limited geographic spaces would be an entirely comfortable proposition. To put it more bluntly, we might have a number of friendly-fire incidents and shoot down each other’s planes. Even more concerning, if Iran had not actually attacked their territories, Saudi Arabia and the UAE might prefer to avoid striking Iran themselves first — since once the hostilities ended, they would have to coexist in the same neighborhood again. For that and other reasons, it is not completely clear that we could count on regional allies to do more than the very important but still limited task of protecting their own airspace. We could hope for more, but should not count on it for force-planning purposes. A similar logic would apply to Japan in the event of any war against China over Taiwan.

Britain can be counted on for a brigade or two — five thousand to ten thousand troops, perhaps — for most major operations that the United States might consider in the future. Some new NATO allies like Poland and Romania, and some aspirants like Georgia, will try to help where they can, largely to solidify ties to America that they consider crucial for their security. The allies also may have enough collective capacity, and political will, to share responsibility for humanitarian and peace operations in the future, though here frankly the record of the entire Western world including the United States is patchy at best. Numerous countries will contribute modestly to limited and low-risk missions like the counterpiracy patrols off the coast of Somalia. If future naval operations are needed perhaps to monitor or enforce future sanctions on Iran, and if we are then lucky, we may get a few allies to participate. Maybe. But that is about as far as it will go.

The bottom line is that the United States need not, and should not, accept primary responsibility for future military operations of a humanitarian nature, and it should not have to play the preponderant role in most future peace operations. But even if it will not have to be the world’s policeman, it will to an extent have to remain the world’s main security guarantor, or at least the lead player in future coalitions designed to carry out that role — providing heavy combat forces for the most serious scenarios, largely on its own among the Western powers. In specific cases, we can always hope for more help. But for planning purposes, we had best not count on too much of it, beyond what a couple key allies like Britain and South Korea could be expected to provide in substantial amounts for certain scenarios.

Michael O’Hanlon is director of research and a senior fellow in Foreign Policy at the Brookings Institution, where he specializes in U.S. defense strategy, the use of military force, homeland security and American foreign policy. He is a visiting lecturer at Princeton University and adjunct professor at John Hopkins University. O’Hanlon is the author of several books, most recently A Skeptic’s Case for Nuclear Disarmament. His writing has been published in The Washington Post, The New York Times, The Financial Times, The Wall Street Journal, among other publications, and he has appeared on TV or radio almost 2,000 times since 9/11. Before joining Brookings, O’Hanlon worked as a national security analyst at the Congressional Budget Office and served as a Peace Corps volunteer in Congo/Kinshasa (the former Zaire). He received his bachelor, masters, and doctoral degrees from Princeton, where he studied public and international affairs.