NATIONAL HARBOR, MD - SEPhTEMBER 20: Secretary of Defense Jim Mattis (L), shakes hands with Air Force Chief of Staff, Gen. David L. Goldfein before delivering the keynote address at the Air Force Association 2017 Air, Space and Cyber Conference, at the Gaylord National Resort and Convention Center on September 20, 2017 in National Harbor, Maryland. (Photo by Mark Wilson/Getty Images)
NEW YORK, NY - SEPTEMBER 19: U.S. President Donald Trump addresses the United Nations General Assembly at UN headquarters, September 19, 2017 in New York City. Among the issues facing the assembly this year are North Korea's nuclear developement, violence against the Rohingya Muslim minority in Myanmar and the debate over climate change. (Photo by Drew Angerer/Getty Images)
In a photograph taken on April 7, 2012, soldiers of the Ground Self-Defense Force set Patriot missiles at the Defence Ministry in Tokyo. Japan has deployed missile batteries in Tokyo and dispatched destroyers carrying interceptor missiles as it boosts its defences against a planned North Korean rocket launch this month. JAPAN OUT AFP PHOTO / Jiji Press (Photo credit should read JIJI PRESS/AFP/GettyImages)
TOPSHOT - A man watches a screen showing a graphic of a North Korean missile launch, at a railway station in Seoul on September 15, 2017.
North Korea fired an intermediate range ballistic missile eastwards over Japan and into the Pacific on September 15, the US said, its latest provocation amid high tensions over its banned weapons programmes. / AFP PHOTO / JUNG Yeon-Je (Photo credit should read JUNG YEON-JE/AFP/Getty Images)
HAMBURG, GERMANY - JULY 07: In this photo provided by the German Government Press Office (BPA), Donald Trump, President of the USA (C) meets Vladimir Putin, President of Russia and President of the EU Commission Jean-Claude Juncker (L) during the G20 Summit on July 7, 2017 in Hamburg, Germany. The G20 group of nations are meeting July 7-8 and major topics will include climate change and migration. (Photo by BPA via Getty Images)
Iranian Revolutionary Guards drive speedboats during a ceremony to commemorate the 24th anniversary of the downing of Iran Air flight 655 by the US navy, at the port of Bandar Abbas on July 2, 2012. The plane was shot down by mistake over the Gulf by the US navy's guided missile cruiser, USS Vincennes, during confrontation with Iranian speedboats on July 3, 1988, killing 290 civilian passengers and crew members. AFP PHOTO/ATTA KENARE (Photo credit should read ATTA KENARE/AFP/GettyImages)
A Yemeni man carrying a gun walks past graves in a cemetery in the capital Sana on June 25, 2017 after the Eid al-Fitr prayer, which marks the end of the holy month of Ramadan. / AFP PHOTO / Mohammed HUWAIS (Photo credit should read MOHAMMED HUWAIS/AFP/Getty Images)
Members of Iraq's elite Rapid Response Division hold upside-down the black flag of the Islamic State (IS) group as they patrol in the Shifa neighbourhood, on the west bank of Mosul, on July 1, 2017, where they are battling some of the last members of the Islamic State (IS) jihadist group in the city. / AFP PHOTO / Fadel SENNA (Photo credit should read FADEL SENNA/AFP/Getty Images)
EAST COAST, SOUTH KOREA - JULY 29: In this handout photo released by the South Korean Defense Ministry, U.S. Army Tactical Missile System (ATACMS) and South Korea's missile system firing Hyunmu-2 firing a missile into the East Sea during a South Korea-U.S. joint missile drill aimed to counter North Korea¡¯s ICBM test on July 29, 2017 in East Coast, South Korea. North Korea launched another test missile, believed to be an Inter Continental Ballistic Missile (ICBM), which travelled 45 minutes before splashing down in the Exclusive Economic Zone (EEZ) of Japan. (Photo by South Korean Defense Ministry via Getty Images)