The atomic bombs in 1945 were deadly and destructive in Hiroshima and Nagasaki. Were the key to defeating Japan and a legitimate use to end a long and bitterly fought war. Negotiations failed to end Japanese military expansion in East Asia Japanese objectives were totally incompatible with United States objectives. Japan attacked Pearl Harbor to cripple the United States military establish an impenetrable defensive perimeter that would force the United States to sue for peace. The United States vastly increased its military capability first for defensive purposes but later to go on the offensive defeat Japan and achieve peace. Atomic bombs are still controversial and people questioning President Truman's decision. Alternatives did exist each with costs and consequences. Each will be considered in terms of morality legality and necessity. The conclusion is based on the results achieved with using two atomic bombs against Japan.