What was the most significant factor in president Harry S. Truman desicion to drop atomic bombs on japan?

Answer 1

The estimated military deaths for an invasion of Japan mandated the use of atomic weapons.
During development of the bomb Germany was seen as also developing the same technology. This lead to a rapid development of the American Project.

As the War progressed it was noted that the Japanese military would fight to the death rather than be taken prisoner or surrender.

The US administration took this in to consideration when planning the invasion of Japan.

The projected losses of American and Allied personnel were Horrific.

A short time after the US and Allied bombers finally were based close enough to conduct Bombing Missions over The main Islands of Japan the Atomic Bomb became available.

The last thing that the Truman administration considered was the way the Japanese Civilian Population had committed suicide rather than surrender. Some alarmist predictions said half the civilian population would suicide or die fighting the invading forces.

Simple math on these projections said that if both available Bombs were used on population centres the loss of life would be comparable or less than the projected losses to the Invading US and Allied forces.

The Japanese Losses would just make the loss of life many times worse.

Truman thought he was doing the least bad thing possible to end the war.

Right or Wrong, the Dropping of two Nuclear Bombs did finally get the Japanese to Surrender.