Why did having Soviet Union as an ally contradict one of the reasons for the United States involvement in the war?

As Allies, if one country were to attack your ally and your ally request your help to battle them your country must or it will break the promise and treaty they signed so they can be allies but Pearl Harbor was the best reason and main reason the U.S join the Allies in WW2

kind of thinking it would be c hope this out

a is your answer

have a great day

may i be brainliest?

~courtney