Hiroshima and Nagasaki
Franklin Roosevelt died suddenly on April 12, 1945, and Harry Truman became president. Many Americans believed he was unqualified for the job. One person said, “If Harry Truman can be president, my neighbor can be president.” This “common man” would make the most important decision of the twentieth century.
America was winning the war against Japan, but the Japanese were fighting valiantly. The enemy would not be defeated unless the American army invaded Japan. Experts concluded more than one million Americans would die in the assault on the Japanese home islands.
Some people urged the president not to use the atomic bomb on Japan. General Dwight Eisenhower was the commander of the Allied forces in Europe, and would eventually succeed Truman as president. Eisenhower opposed the bomb for two reasons. “First, the Japanese were ready to surrender and it wasn’t necessary to hit them with that awful thing. Second, I hated to see our country be the first to use such a weapon.”
President Truman gave the order to drop an atomic bomb on the Japanese city of Hiroshima in August 1945. Even after testing, the American scientists were unsure of what would happen. The Americans thought about warning the Japanese first, but the enemy might have moved Allied prisoners to the site. The Americans rejected dropping the bomb in the ocean. They decided the war would not end unless the Japanese government understood the damage America would inflict.
The world entered the frightening atomic age at 8:14 a.m. local time in the Japanese city of Hiroshima. One minute later, an atomic bomb destroyed the city. The first flash of the explosion was as bright as a thousand suns. It is estimated that 80,000 people were instantly vaporized. The blast created violent winds that caused firestorms. Co-pilot Robert Lewis said he could taste the atomic fusion. He later wrote in his journal, “My God, what have we done!” Another member of the crew said, “Thank God the war is over and I don’t have to get shot at. I can go home.”
Truman later said he did not agonize over using the bomb. He wanted to make Japan surrender without an invasion. “The atom bomb was no ‘great decision,’” he later said. “That was not any decision you had to worry about.” A second bomb destroyed the city of Nagasaki. Japan agreed to surrender a week later.

Japan surrenders (headline)
Resources
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Mr. Donn has an excellent website that includes a section on World War I and World War II.

The mushroom cloud that followed the dropping of the second atomic bomb on Nagasaki, Japan on August 9, 1945.

President Harry S. Truman (1884 – 1972) succeeded to the presidency when Franklin Roosevelt died in 1945.

One person later wrote of the aftermath of the bombing, “a good deal has been written about Hiroshima, but no-one can describe adequately the smell — and the flies.”

Representatives of the Japanese government formally surrender on board USS Missouri September 2, 1945.