The List: The Next Nuclear States

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Virtually there: Japans advanced civilian program could probably produce weapons within months. Japan

What it has: Twenty-three tons of weapons-usable plutonium and the ability to produce weapons-grade uranium without much trouble. Sometimes described as a virtual nuclear weapons state, Japan has one of the worlds largest and most advanced civilian nuclear programs. It could likely have nuclear weapons within a few months of deciding it wanted them.

Why go nuclear: The only nation ever to have nuclear weapons used against it, Japan has long been staunchly anti-nuclear. But the country has also grown increasingly nervous about what it sees as deteriorating regional security. North Koreas great leap may tip Japanese public opinion, and some politicians are calling for the country to debate openly whether it should have nukes. The country could withdraw from the Non-Proliferation Treaty with three months notice by claiming its supreme interests are at risk.

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Defiance: Iranian President Mahmoud Ahmadinejad opens a heavy water plant in August 2006. Iran

What it has: No one knows for sure. Most estimates suggest that Iran is five to 10 years away from being able to produce weapons-grade uranium and plutonium. But it has a history of using foreign sources of technology and equipment, as well as the nuclear black market, to pursue those materials. And its expertise has often been underestimated in the past. Its missiles are capable of delivering nuclear warheads to Israel or southern Europe, and it allegedly bought six cruise missiles from Ukraine in 2000 that are designed to carry 200-kiloton nuclear warheads.

Why go nuclear: Iran makes no secret of the fact that it wants to be the preeminent power in the Middle East. And it may be emboldened to accelerate its pursuit of nuclear weapons if North Korea gets only a slap on the wrist for its recent test. Domestically, both conservatives and reformers support their countrys right to develop nuclear technology, and many Iranian military leaders see nukes as a necessary supplement to Irans less-advanced conventional forces, which have been hampered by U.S. sanctions.

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Heavy load: Taiwans fourth nuclear plant, set to go online in 2009, comes together. Taiwan

What it has: As recently as the late 1980s, Taiwan was within a few years of becoming a nuclear-armed state. But the United States and others insisted it back down. Taiwan now has no uranium enrichment capability, and its sole facility for handling plutonium was torn apart. Its weapons-grade remnants likely include fewer than five pounds of plutonium and two tons of uranium. But its scientific know-how has probably survived.

Why go nuclear: As the military balance between China and Taiwan tilts increasingly in the mainlands favor, Taiwan could decide that it needs nukes to restore equilibrium fast. Like North Korea, Taiwan can argue that it faces an existential threat from a superpower.

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Not me: Syrian President Bashir al-Assad claims he doesnt want nuclear weapons. Syria

What it has: Most experts dont believe Syria is attempting to develop nuclear weapons. It did, however, acquire a civilian nuclear reactor from China in 1991 and a light-water reactor from Russia in 1999. The relationship with Russia has fueled speculation that Syrias nuclear intentions are not pure, as have its missile purchases from North Korea and Pakistan.

Why go nuclear: Perhaps no state is watching developments in Iraq, Iran, and North Korea more closely than Syria. If Iran and North Korea use the threat of nukes to deter the United States, Syria (which suspects its in the superpowers cross hairs) may decide that it has little choice but to follow suit. Syrian leaders are also keeping a close eye on nuclear developments in Egypt and Saudi Arabia. If one or both nations go nuclear, Syria may decide to keep pace.

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Oops: Workers dismantle an experimental reactor in South Korea after revelations arose about secret research. South Korea

What it has: South Korea probably cant produce weapons-grade plutonium or highly enriched uranium, despite having an advanced civilian nuclear sector. It did, however, secretly pursue nukes in the 1970s, and its scientists were researching clandestinely as late as 2000. And it could always import technology from elsewhere.

Why go nuclear: People in Seoul have long claimed they dont view the North as a military threat, but perceptions are certainly shifting. And with heightened U.S.-South Korea tension, Seoul has shown increasing interest in developing a defense capability independent of the United States. On the other hand, it may just wait to see whether eventual reunification allows it to inherit North Koreas nukes.