World War II
Hard times overseas led to the rise of dictators who wanted to conquer other countries. European countries began forming alliances, and much of the world became involved in another major war.
By June 1941, German forces had attacked France and the Soviet Union. The United States stayed out of the war until the Japanese bombed Hawaii.
While fighting was ongoing in Europe, battles raged on in Asia. Fearing that an invasion of Japan would cost many American lives, President Harry Truman decided to drop the atomic bomb on Japan to force Japan to surrender.
World War II left behind record high casualties and deadly new weapons.