Thats a pretty general question, and I assume the answer varies depending on which WWII board game you are playing. I personally can’t speak regarding other games (Global War 1936, War Room, Triumph and Tradgedy)… I can only speak about my experience with various versions of axis and allies.
Most of the axis and allies variant games I played this year lasted very long (7 or more full rounds) and were fought to a stalemate, with the axis player eventually conceding that they were going to lose in the long-run.
The original classic A&A, revised A&A, and A&A europe 1940 2nd edition often seem to boil down to this: If axis powers take moscow, the game is pretty much over. If the allies conquer either Berlin or Tokyo, the game is pretty much over. Its rarely necessary to continue once either of those conditions is met, because the income bonus and momentum is hard to overcome.
I would say that most games I play end in less than 10 rounds.
