OK thanks, guys.
That seems a huge rift, though doesn't it? Two branches of Judaism from two millennia ago believing two different things about a rather important issue and one coming out on top for - it seems - no other reason than they were the ones left standing.
Is it like Christianity, where there were all flavors of Christianity about, Marcionism, Gnosticism, etc, and the one that came out at the end was simply because the head of the most powerful empire at the time 'picked a side' basically and enforced it with laws and violence?