Edit: Reading your comments again, it does look like you are a pacifist?
> I think it's ok to take life if it's your own life or help someone to take their own if there are good reasons for it.
I read this as you think it is never OK to take a life in self defence, even if that means that tens of millions will be exterminated?
If so, you can disregard the rest:
> Figting and killing didn't help them in any way.
There are also many examples of much smaller ethnic groups who avoided complete extermination because they had a very competent army.
If you don't resist a neighbor who wants to exterminate your ethnic group, then the outcome is given. If you do resist, you still have a chance.
> The rest of the populace would just become the part of their (WW2 Germany) empire.
No. That is only true for northern and maybe western europe. Eastern europeans were considered vermin by them.
> They were multitude of ethnic groups who survived by getting assimilated into their stronger neighbors.
That can happen. Doesn't mean it's a given. I feel your overall logic reasoning leaves a lot to be desired? Do you strive to make logically sound arguments, or is that not important? If not, I don't think we can take this any further.
There is a sliding scale here. You have everything from pressure to align your country with the bigger neighbor all the way down to 100% extermination.
Germany's plans for the Slavic peoples were complete extermination. There was nothing the slavs could do or say to convince the German leadership to change their mind.
> I'm Polish. How much good do you think killing Germans did for Polish people in 1940?
Maybe you think that Germany didn't plan to exterminate all poles. Ok, let's just pretend that's the case. By advocating that Poland shouldn't have resisted, you're at the same time advocating handing over the 3 million Polish jews to Germany without a fight, knowing what would happen to them. Are you really OK with that?
> Stalin is a different thing. Just because Russians are terrible at everything. I'm still sure they wouldn't manage to keep whole Europe under their shoe for long. And if they did that would mean they seriously stepped up their game, so prosperity of sorts.
Sure, the Russians would have had a hell of a time keeping western europe under control. Stalin's answer to such problems were simply killing enough people until the problem disappeared. Not letting them do their own thing.
During the 1930's, Stalin sent out his underlings with orders to kill a certain quota in given area. The quotas were in the hundreds of thousands.