It's funny because if you go to WWI you can see a pretty clear example of what happens when socialists pitch in with the imperial powers in their power struggles. It doesn't end in success for the left. WWII is a special case because it did in fact feature a socialist option and so a contribution to the war effort meant a contribution to the protection of that fledgling socialist project. That said, if you were a commie in either the UK or US who aided in the war effort what did you get in return? Liberal powers drafting Nazis into the new NATO organization and disenfranchisement via red-scare within your own nation. That's why my point is that denazification doesn't exist under liberalism, the fascists are born from material conditions that liberalism cannot by definition change. So even a liberal victory over fascism ultimately results in fascism re-emerging at a later date. It's only redistributive and socialist political projects that stomp out the root of fascist ideology and actually complete the goal of denazification. As an individual in war time? Help those around you and protect the people you can. But as a larger left project getting co-opted into the liberal project of imperialist wars doesn't do us any good

The position of the COMINTERN at the time prior to the fascist invasion of the USSR, was that it was an inter-imperialist conflict that was going to drag the USSR into it at one point or another - the question at that point of time was a matter of "how long can we delay the inevitable" and "when most likely are we going to enter the conflict".

It was at this point we saw the Communist movements in Germany, Italy, Spain, Hungary, Romania, Czechoslovakia, Poland, France, Denmark, Norway, Greece, Yugoslavia, Albania, Bulgaria, Belgium, Luxembourg, Netherlands, etc. squashed to varying degrees with refugees fleeing outwards from the newly installed regimes, and the USSR happened to recieve a decent amount of them due to their proximity. And with those refugees came stories of the union busting, labor rights slashing, capitalist looting, the whole nine yards. There was a tacit understanding that a confrontation between the Communists and the anti-communists was inevitable, that you would need to have your head buried in the sand to not notice it.

Of course in the lead-up to the moments before the fascist beasts swallowed up many countries the position of the comintern stilled followed revolutionary defeatist action and that the Communist parties of their respective countries were expected to combat capitalism and social-chauvinists that muddy the waters of Marxist ideology. After countries started to fall one-by-one, the comintern shifted to forming all-socialist united fronts with all the socialist ideological strains to combat the surging tide of fascism, to later forming popular fronts with the capitalists threatened by the fascists to strategically collaborate against the greater threat. This meant the usual ideological combat between communists and capitalists were put on the backburner, and temporary class collaboration was permitted until the fascist threat was extinguished.