They did not want to get involved. American practiced isolationism - unless the war involved them (which both didn't) they didn't interfere.
Explanation:
They only entered World War One because of the Zimmerman Telegram where Germany encourage Mexico to open fire on the USA, and the only reason we got into World War Two was because Britian was begging for us to enter.
Within a week of Pearl Harbor the United States had declared war on the entire Axis, turning two previously separate conflicts into a true world war. ... In November, the first American combat troops entered the European war, landing in French Morocco and pushing the Germans east while the British pushed west.
