The most likely reason why President Truman ordered the atomic bomb dropped on Japan was to

Truman’s stated goal was to end the war quickly by compelling Japan to surrender to the Allies. Japan’s leaders had not yet surrendered, and the United States expected the atomic bomb’s devastating impact to make continued resistance untenable. Preventing Soviet influence and demonstrating U.S. power are sometimes discussed as additional considerations, but the best answer is to force Japan to surrender.

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