President-elect Donald Trump tweeted that the US needed to "expand its nuclear capability." When he was later asked about the tweet by "Morning Joe" host Mika Brzezinski, Trump responded "let it be an arms race."
On July 16, 1945, the US conducted the world's first test of a nuclear weapon. Less than a month later, two bombs were dropped on the Japanese cities of Hiroshima and Nagasaki, bringing about the end of World War II.
No nuclear bombs have been used as weapons since the attacks on Japan, but thousands of tests have been conducted — primarily by the US and USSR throughout the Cold War.
Alex Kuzoian contributed reporting to an earlier version of this article.
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