To ensure that the United States developed a bomb before Nazi Germany, the federal government started the secret $2 billion Manhattan Project. On July 16, 1945, in the New Mexico desert near Alamogordo, the Manhattan Project’s scientists exploded the first atomic bomb.

It was during the Potsdam negotiations that President Harry Truman learned that American scientists had tested the first atomic bomb. On August 6, 1945, the Enola Gay, a B-29 Superfortress, released an atomic bomb over Hiroshima, Japan. Between 80,000 and 140,000 people were killed or fatally wounded. Three days later, a second bomb fell on Nagasaki. About 35,000 people were killed. The following day Japan sued for peace.

President Truman’s defenders argue that the bombs ended the war quickly, avoiding the necessity of a costly invasion and the probable loss of tens of thousands of Americans lives and hundreds of thousands of Japanese lives. His critics argue that the war might have ended even without the atomic bombings. They maintain that the Japanese economy would have been strangled by a continued naval blockade and forced to surrender by conventional firebombing or by a demonstration of the atomic bomb’s power.

The unleashing of nuclear power during World War II generated hope of a cheap and abundant source of energy, but it also produced anxiety among large numbers of people in the United States and around the world.