From a Marxist perspective, UK, USA, France etc had the same class interests as Nazi Germany. They were also uncomfortably okay with the Nazis Pre-war. I know this is a big topic (and I’m sure some marxist books have been written on it) but briefly why did the Allies fight against Nazi Germany from a dialectical pov.
They liked when Hitler talked about killing the Soviets, but they hated the idea of Germany returning to the great powers race. WW2 was an extension of the inter imperial conflicts in WW1. The allies stepped up the war and invaded France when it looked like the Soviets were going to occupy all of Germany.
There was a struggle to contain Germany, hence the pacts between the French, Brits, and Poles. They also wanted Germany and the USSR to partake in mutual destruction, WW1 again, but just in the east.