Kim Jong Un Kim Jong Un

North Korean Foreign Minister Ri Yong Ho leaves his hotel in New York on Monday. Ri says President Trump's tweets amount to a declaration of war against North Korea — and that the country can now defend itself under international law. Jewel Samad/AFP/Getty Images hide caption

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Jewel Samad/AFP/Getty Images

TV screens at a store in Seoul, South Korea, show news coverage of the latest exchange of insults between President Trump and North Korean leader Kim Jong Un. Ahn Young-joon/AP hide caption

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Ahn Young-joon/AP

In May 1962, the U.S. conducted its first and only test of a nuclear-tipped missile. Some worry North Korea could try something similar. United States Navy /Science Faction/Getty Images hide caption

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United States Navy /Science Faction/Getty Images

How North Korea's Nuclear Tests Could Get Even More Terrifying

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The government of North Korean leader Kim Jong Un conducted two nuclear tests last year. Wong Maye-E/AP hide caption

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Wong Maye-E/AP

North Korea Claims Successful Hydrogen Bomb Test

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Passers-by look at the North Korean missile's path over Japan, displayed on a huge screen in Tokyo on Wednesday. Japanese Prime Minister Shinzo Abe said he and President Trump have agreed to increase pressure on Kim Jong Un's regime after it launched a ballistic missile over the Japanese island of Hokkaido. Toshifumi Kitamura/AFP/Getty Images hide caption

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Toshifumi Kitamura/AFP/Getty Images

Afternoon traffic passes in front of a wall painted with the flags of the U.S. and Guam in the Tumon district on the island of Guam on Friday. The island has become a talking point in the rhetoric coming from President Trump and North Korea. Virgilio Valencia/AFP/Getty Images hide caption

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Virgilio Valencia/AFP/Getty Images

A man looks at images depicting missile launches and military exercises, on a display board in Pyongyang, North Korea, earlier this week. Ed Jones/AFP/Getty Images hide caption

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Ed Jones/AFP/Getty Images

South Korean soldiers in Seoul walk by a TV news program showing a file image of a missile being test-launched. North Korea on Tuesday test-launched another ballistic missile in the direction of Japan, U.S. and South Korean officials said. Ahn Young-joon/AP hide caption

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Ahn Young-joon/AP

Tillerson Confirms North Korea Missile An ICBM, Calls For Global Action

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The North Korean flag flies above the country's embassy in Beijing last month. China is the North's most important trading partner and ally, but lately Beijing has been placing pressure on Pyongyang over the North's nuclear and missile programs. Mark Schiefelbein/AP hide caption

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Mark Schiefelbein/AP

North Korean leader Kim Jong Un attends the combined fire demonstration of the services of the Korean People's Army in celebration of its 85th founding anniversary in a photo released on April 26. KCNA via KNS /AFP/Getty Images hide caption

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KCNA via KNS /AFP/Getty Images

An official photograph dated April 15 and posted by the Navy shows the aircraft carrier USS Carl Vinson in an Indonesian strait thousands of miles south of North Korea. MC2 Sean M. Castellano/U.S. Navy hide caption

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MC2 Sean M. Castellano/U.S. Navy