I.

Why is there such a strong Sunni/Shia divide?

I know the Comparative Religion 101 answer. The early Muslims were debating who was the rightful caliph. Some of them said Abu Bakr, others said Ali, and the dispute has been going on ever since. On the other hand, that was fourteen hundred years ago, both candidates are long dead, and there's no more caliphate. You'd think maybe they'd let the matter rest.

Sure, the two groups have slightly different hadith and schools of jurisprudence, but how many Muslims even know which school of jurisprudence they're supposed to be following? It seems like a pretty minor thing to have centuries of animus over.

And so we return again to Robbers' Cave: