Final answer:
President Truman authorized the use of atomic bombs to end World War II quickly and to avoid the high American casualties projected for a traditional invasion of Japan. Advised by military leaders and amidst geopolitical considerations, including the looming Cold War with the Soviet Union, the bombings of Hiroshima and Nagasaki were seen as necessary to expedite Japan's surrender.
Step-by-step explanation:
President Truman faced a difficult decision when considering the use of atomic bombs on Japan. With estimates suggesting up to 250,000 American deaths in a potential invasion of Japan, Truman saw the atomic bomb as a means to an immediate end of World War II with fewer Allied casualties.
The Manhattan Project, unknown to him until he became president, developed the nuclear weapons that ultimately led to Japan's surrender. Truman's decision was supported by an advisory committee, despite the controversial morality of such an action. The first bomb, "Little Boy," was dropped on Hiroshima on August 6th, and the second, "Fat Man," on Nagasaki three days later, hastening the end of the war.
Some military leaders believed Japan was on the brink of surrender due to the naval blockade and fire-bombing campaigns, suggesting the atomic bombs were unnecessary. However, the potential Soviet incursion and political posturing for the emerging Cold War may have influenced Truman's decision to deploy the second bomb swiftly.
Truman's directive was an intersection of military strategy and geopolitical maneuvering, made in the belief that it would conserve American lives and resources. While historical analysis reflects differing perspectives, the deployment of nuclear weapons marked a decisive, albeit controversial, end to the conflict.