Residents watch a big video screen on Mirae Scientists Street in Pyongyang showing newsreader Ri Chun-Hee as she announces the news that the country has successfully tested a hydrogen bomb on September 3, 2017.
North Korea declared itself a thermonuclear power on September 3, after carrying out a sixth nuclear test more powerful than any it has previously detonated, presenting President Donald Trump with a potent challenge. (KIM WON-JIN/AFP/Getty Images)

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