President Truman believed that dropping the atomic bombs saved both American and Japanese lives because a battle on mainland Japan would have been devastating.
He is supported in this stance by the fierce resistance of the Japanese on islands closer to the mainland such as Okinawa. With over a million more Japanese soldiers waiting on the mainland as well as thousands of Kamikaze pilots, resistance on the Japanese mainland was going to be very brutal and would potentially have cost millions of lives, both civilian and military.
Truman therefore believed that dropping the atomic bombs would cause the Japanese to surrender and save both nations the massive loss of life.
