> For the first 3 years of WW2 USSR was an ally of nazis.

This sounds inaccurate or at best an oversimplification of the complicated pre-WW2 treaties flying all over europe. I only see this idea in reference to the Molotov–Ribbentrop Pact, but that only lasted 2 years and was a non-aggression pact, not an alliance. But maybe you are talking about a different agreement?

Can we talk about actions as well, not only written agreements?

You had a chance to. The gp did too. You did not take it yet and instead asked my permission. Thank you, I guess. Go ahead, you may.

What non-aggression??? USSR and Germany partitioned Poland in 1939

https://en.wikipedia.org/wiki/Occupation_of_Poland_(1939%E2%...

Thanks! I was looking at stuff that lasted the mentioned 3 years which I couldnt track to anything, and grouped the Poland invasion as part of this pact, though it's worth mentioning separately.

Fwiw, Non-aggression pact means no aggression against each other but it was an coordinated invasion of Poland, so your right.

> For the first 3 years of WW2 USSR was an ally of nazis.

Let's not forget Finland.