TL help: pre-Islamic India

I'm doing some preliminary research for a TL where Persia and Byzantium set aside their differences (temporarily) to fight off the Islamic hordes... I've got the scenario for Europe down pretty well in my head (Visigothic kingdom survives, Byzantium of course survives... I might even have Frankia continue), but I didn't want this timeline to be as Europe-based as OTL. I had the idea of a strong Hindu empire based in India becoming a great power and colonizing various parts of the world. Does anybody know of a good resource for info on the various Indian states before the coming of Islam?
 
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