President harry truman justified using atomic bombs on japan in 1945 on the grounds that the

President Truman justified the use of atomic bombs on the grounds that doing so saved many lives.  In a radio address he gave prior to Japan's final surrender, he said that the use of atomic weapons was chosen "in order to shorten the agony of war, in order to save the lives of thousands and thousands of young Americans." 

Notice that Truman's rationale speaks mostly to loss of life by American soldiers if a war on the ground were pursued in Japan.  It does not as much take into account Japanese lives, though many Japanese soldiers would also have lost their lives in conventional warfare if that were pursued.  But the atomic bombs killed an estimated 150,000 persons in Hiroshima and an estimated 75,000 persons in Nagasaki in a very short time.  Added to that would be all sorts of other health effects that contributed to sickness and early death to many more people due to radiation from the bombs.  Many people still question the ethics of using the bombs rather than pursuing other alternatives for ending the war.