The atomic bombings that resulted in the deaths of hundreds of thousands of Japanese civilians were regrettably and truly horrible events. However, Japan was not going to surrender easily. If the atomic bomb had not been used as a strategic weapon, an invasion of Japan, Operation Downfall, was planned, which would have been the largest military operation in history. Americans would have fought the Japanese on their home soil, and the Japanese knew right where the invasion forces would be landing. U.S. casualties would very likely have been massive, in the hundreds of thousands. American intelligence thought that the Japanese had about 2,600 aircraft to use against the U.S. Navy ships. However, after the surrender, almost 13,000 planes were found. Most of them were hidden, including 25 to 35 jet aircraft. The Japanese strategy would have been to send wave after wave of kamikazes, 300 to 400 at a time, to inflict heavy casualties on the troop ships before a single American soldier or Marine ever set foot on the beach. General George Marshall (at that time the equivalent of Chairman of the Joint Chiefs of Staff) wanted to wait and use several atomic bombs as battlefield tactical weapons prior to the invasion, which would have resulted in tens if not hundreds of thousands of American troops being exposed to radiation, giving them radiation sickness. The invasion would have been a logistical nightmare, and could have collapsed under its own weight. So, President Harry Truman decided on the use of the atomic bombs because of the enormous cost in life from an invasion.
I would refer everyone to the following book:
Hell to Pay: Operation Downfall and the Invasion of Japan, 1945-1947 (Revised Edition), by D. M. Giangreco, published 2017
