In 1945, the United States and Japan fought for four years in the Pacific War.
On July 26 of that year, the president of the United States, Harry Truman, issued an ultimatum against the Japanese. He demanded unconditional surrender, otherwise swift and total destruction awaited them.
On August 6, 1945, the United States dropped the first bomb on Hiroshima, this bomb was called Little Boy. On August 9, 1945 the second bomb was dropped on Nagasaki, this bomb was called Fat man.
Finally, Japan declares itself defeated on August 14, 1945.

