These related questions may be of interest:

• How long has the concept of a "War Crime" existed? : AskHistorians, answer by /u/ThePurplePantywaist
• Why weren't the bombings of Hiroshima and Nagasaki considered war crimes? The United States wiped out hundreds of thousands of Japanese civilians. Was this seen as permissable at the time under the circumstances? : AskHistorians, by /u/restricteddata
• Why isn't the bombing of Hiroshima and Nagasaki considered a war crime? : AskHistorians
• Why are the bombings of Hiroshima and Nagasaki not considered war crimes ? : AskHistorians
• Was the US ever tried for dropping the Atomic Bomb on Nagasaki and Hiroshima? : AskHistorians
• Is it true that the U.S. dropped flyers around Japan as a warning to the Japanese civilians before they bombed Hiroshima and Nagasaki? : AskHistorians
• What types of war crimes were committed by invading allied soldiers in Europe in WWII? : AskHistorians