Kim Jong Un Kim Jong Un

Kim Jong Nam had been critical of North Korea's dynastic rule. Kim Jong Un, who inherited the leadership in 2011, was believed to have issued a standing order for his brother's execution. Asahi Shimbun via Getty Images hide caption

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Asahi Shimbun via Getty Images

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