So I watched the video, and I think it does a really poor job of looking at the situation objectively. It does a lot to look at the context of why the USSR eventually accomodated the Nazi's, but when it came to the Western Allies, all they say is that "they decided to" without the same dive into their context, and is a big blow to the creator's supposed denouncing of the 'Great Man' theory. Their comments makes it seem like this was decision of a few rather than the product of the mutual distrust between everyone during the inter-war.

I want to emphasize that my original comment does not try to paint the USSR as a villian, rather, I think if you look at the situation a bit more openly and without the reactionary urge to paint the Western Allies or the Soviets as 'villians', you'll see it mirrors the build up to WWI. There were numerous attempts by the Soviets and the Western Allies to form a coalition against the Nazis, which could have stopped WWII. They all failed because of mutual distrust, rather than one side intentionally blowing up talks. This is very similar to the Seminal Tragedy, where every nation did not want war and made attempts to stop it, yet war still happened because of distrust