IF The United States hadn't entered WWII?

Hey everyone.
I am by no means well-acquainted with the events of World War II, it's always fascinated and inspired me, but my education on the subject is the proud child of the California School System, which should say a lot.

So, the question I pose may be controversial, but I do not, by any means, intend to offend any nation or WWII part-taker with it.

History classes went over WWII, but usually it was a very textbook view on the war, without any ifs, what could have or would have beens, etc.

So, maybe a few of the buffs on this forum can indulge me in the possibilities of the US not entering the war. If I recall correctly from class discussions, the Russian front was beginning to look better after Stalingrad, and the Russians were pushing forward, but would the same fate we know today be met by the Nazi Germans had the US Not entered the war?

Sorry if this is a thoroughly discussed topic, I tried the search button and google but didn't find much.
Thanks for the knowledge.