Development of Religion Without Islam?

[CandyDragon]

From this thread.

I'm wondering how would a lack of Islam affect the development of religion. For instance, without Islam, what happens to Christianity- how does it evolve without a significant enemy, except, arguably, Zoroastrianism, which seemed to be propped up by the Sassanid State by the time Islam came round. Does Christianity turn against itself?

What about the development of Northern India? Without the Mughals, and the various Delhi Sultanates, what happens to Hinduism? It obviously butterflies the Sikhs, but how would India look, religiously speaking today?

Obviously these are just a few of the many questions that would need to be asked about suc a scenario.