In WWI the US finally intervened as Germany pursued unrestricted submarine warfare, directly ignoring US wishes. However, the US also realized that continental

In WWI the US finally intervened as Germany pursued unrestricted submarine warfare, directly ignoring US wishes. However, the US also realized that continental europe ignoring US wishes would be the default regardless of which party won. If Berlin won then the combined nation would be able to gain domination of the seas and therefore global trade. If the allied won, then they would have excluded america from world trade to rebuild their economies. As for WWII, the US could have focussed on Japan but instead they had a Europe First strategy which involved denying nazi germany european hegemony. However, by the time they actually decided to invade it was clear Germany was already defeated by the soviets and it was a matter of time.