Recently, Dr De Weerdt mentioned one of the consequences of the Battle of Talas, in which the Chinese and Arabs fought each other for world domination in AD 751, was that the land routes for trade via central Asia were closed. This according to her was one of the primary reasons for trade to shift to sea routes.
That theory fits quite well with the fact that the next three centuries were the glory days of Tamil civilisation. Simply by virtue of geography — sitting as it did in the middle of these traders from Arab regions and China — the Tamil country became extremely prosperous. It was also the period of Cholas at their height of their naval might and their fine bronzes. As Peter Francis notes in Asia’s Maritime Bead Trade: 300 B.C. to the Present, Tamil poetry from earlier and extending to this period discusses how the ships brought in gold to take pepper.
Remember this was also the period revival of Hinduism happened in much of what’s now India. As Dr De Weerdt noted, the plains of India were no longer the centre of Buddhist thought as they had been for few centuries until then. That must have meant there was already very little reason for Chinese and Japanese to come to India as they once did in large numbers resulting in spread of ideas. The closed land routes after AD 751 must’ve therefore isolated what’s North India for the same three centuries. Getting there was hard and there wasn’t much reason to. Japan and China were the new centres of Buddhist thought.
It’s amusing to think in the time of a Prime Minister who’s a Swayamsevak that the revival of Hinduism is possibly what caused the decline of India; and quite likely contributed to Muslim invasions a few centuries later. If Buddhism had reigned supreme, it’s conceivable and quite likely that the history of the world would have been very different. The Arabs wouldn’t have won the Battle of Talas at the least. And we’d all be speaking Mandarin, as well. And have had paper records instead of temple inscriptions from that period. Perhaps the Chola temples would then have not been as magnificent.
 – The discussion can be found here.