Or had joined Hitler against the USSR in 1941.
Nope: I dont go along with that.
Hitler needed killing, but so did Stalin.
But why does the sequence make difference? By joining Hitler the USA coule have killed Stalin and later Hitler by turning on Hilter after that.
I'm no expert in WWII history and, moreover, have no intention to become one, but the USSR engaged 80% of the Hitler's land divisions. This fact worth considering.