America was allies with plenty of nations that were violent expansionist colonial powers, did Americans care that Japan had invaded China or Korea? Could Japan have avoided war with America by not antagonizing the Americans or was war inevitable with Japanese imperial ambitions?
This [answer] (https://www.reddit.com/r/AskHistorians/comments/tqcunt/did_american_leaders_think_that_the_sanctions/) by /u/Myrmidon99 details the enactment and goals of the sanctions against Japan and touches on the origins of them. I believe it's fair to say that there were two different waves of sanctions against Japan in the 1930's and 40's with two interrelated but separate justifications. Japan's invasion of China violated the League of Nations Covenant that was intended to suppress further wars of conquest, and the Nanking Massacre's unapparelled death toll and overall cruelty further poisoned relations between the US and Japan and allowed Roosevelt to enact a moral embargo. The second set of sanctions can be seen as a response to Japan's occupation of French Indochina in 1941 and the fears by the Western powers that Japan would continue to move on the other neutral states and European colonies in the region, allowing the Roosevelt administration to enact sanctions intended to cripple Japan's war effort and hopefully bring them to the negotiating table to cease hostilities.