There was no one specific event that caused Truman to decide to use the atomic bomb where, where without that event he would not have done so.
The US and Japan were at war and were treating each other in what we would now call a barbarous fashion. The invasion of Iwo
Jima
had been much more difficult than expected and had resulted in extremely high US casualties. Military planners thought a conventional invasion of the Japanese Home Islands would result in over a million US casualties and lead to a protracted guerrilla war, with Japanese civilians fighting to the death, etc. That is the sort of calculation that lead to Truman agreeing to use the atomic bomb.
Truman didnt want Stalin to get any peace, and was basically telling him to back off
It was a tough call for the President but he reasoned that he could end the war faster and save the lives of many American service men. The deaths of the military there, helped in that decision.
Bombing or invading Japan
Ending the war with Japan without getting huge numbers of Allied service members killed.
if you drop a bomb on japan, ninjas will die
Based on the information that he had, yes. Japan had refused to surrender, invasion of Japan would have cost several million lives, and it DID end the war.
Truman didnt want Stalin to get any peace, and was basically telling him to back off
to end the war
It was a tough call for the President but he reasoned that he could end the war faster and save the lives of many American service men. The deaths of the military there, helped in that decision.
The most significant factor in President Harry S. Truman's decision to drop atomic bombs on Japan was the desire to expedite the end of World War II and minimize American casualties. Truman and his advisors believed that using the bomb would force Japan to surrender unconditionally, thus avoiding a potentially devastating invasion of the Japanese mainland. Additionally, demonstrating the power of the atomic bomb was seen as a way to strengthen the United States' position in post-war negotiations, particularly with the Soviet Union.
Japan was in total disaster after the atomic bombs and Japan had no remedy what so ever. They had to surrender.
Truman
Truman
Bombing or invading Japan
Japan would not surrender prolonging on the war
Ending the war with Japan without getting huge numbers of Allied service members killed.
The prevention of having to invade and conquer mainland Japan, which by all estimates would have an enormous cost in US casualties and prolong the war with many months, if not with years.