why did truman decide to drop the atomic bomb on hiroshima?

why did truman decide to drop the atomic bomb on hiroshima?
Answer
Brief Explanations:
Several factors influenced Truman's decision. To end the war quickly and avoid a costly invasion of Japan, to demonstrate US military - might to the Soviet Union, and to use a new and powerful weapon that had been developed.
Answer:
To end World War II quickly, avoid a costly invasion of Japan, and show US power to the Soviet Union.