Dropping A-bombs on Hiroshima and then Nagasaki were not pre-emptive. We demanded unconditional sur- render by Japan. The U.S. was winning the war at that point. Since no Aamericans were killed thereafter it is impossible to estimate the number of American lives that were saved by not invading Japan to get it to surrender unconditionally.
U.S. confirms ISIS computer expert killed in air strike (Reuters)