In 1945, Harry S. Truman became President of the United States, inheriting the world’s most powerful weapon: the atomic bomb. He soon faced the critical decision of whether to use it.

The Potsdam Conference and Allied Occupation of Berlin

Truman firmly believed that deploying the atomic bomb was the only way to force Japan to surrender. In August 1945, he ordered atomic bombs dropped on Hiroshima and Nagasaki.

A few days earlier, Truman met with British Prime Minister Winston Churchill and Soviet leader Joseph Stalin near Berlin in Potsdam to discuss postwar peace. The three leaders agreed that the United States, Britain, the Soviet Union, and France would jointly occupy Germany. Truman, deeply distrustful of the Soviet Union, secretly resolved to limit Moscow’s influence over Japan’s postwar future. U.S. forces in Japan were commanded by General Douglas MacArthur, who swiftly acted to try Japanese war criminals and implement reforms that guided Japan toward a Western-style democratic system.

The United States’ Pacific campaign against Japan included decisive victories such as the Battle of Midway in 1942 and the killing of Japanese Admiral Isoroku Yamamoto in 1943. In 1945, the U.S. conducted the Battle of Iwo Jima and executed massive air raids on Tokyo.

On August 6, 1945, the United States dropped the first atomic bomb on Hiroshima. Three days later, a second bomb was dropped on Nagasaki.

Research by the Japanese Radiation Effects Research Foundation estimates that within 2–4 months after the bombings, between 150,000 and 246,000 people died from immediate and radiation-related causes. Facing overwhelming devastation and no remaining options, Japan surrendered in less than a week.