There were numerous historical precedents for the unannounced military action by Japan , but the lack of any formal warning , particularly while peace negotiations were still apparently ongoing , led President Franklin D. Roosevelt to proclaim December 7 , 1941 , " a date which will live in infamy " . Because the attack happened without a declaration of war and without explicit warning , the attack on Pearl Harbor was later judged in the Tokyo Trials to be a war crime
war crime
Japanese war crimes
Attack on Pearl Harbor