Me:
> Stalin only joined WW2 because the Nazis had the hubris to attack the USSR
As I learned sometime after this, from Snyder's Yale lectures about the history of Ukraine, Stalin actually helped Hitler *start* WW2 by invading Poland with him, and occupying a big chunk of it. Strange that this isn't part of the popular narrative if WW2 history.
But my comment here is still fair if applied only to why they started fighting the Nazis.