Here's a generic map of the general historical cultural sphere of India from Wikipedia: upload.wikimedia.org/wikipedia/commons/thumb/0/05/Hinduism_Expansion_in_Asia.svg/1920px-Hinduism_Expansion_in_Asia.svg.png Heavy sea based spread into SE Asia, which makes sense. Despite religious diffusion no spread into China, but the mountains and strong China make this understandable. The lack of direct Western spread also makes sense with the strong Persian and successor states. But why no oceanic spread west to mimic east?

We know routes are reliable to Africa. We know the trade was valued. To a layman government or cultural strength in Africa or Arabia doesn't seem stronger than in SE Asia.. where are the Ethiopian Buddhists? Where are the elephant mounted equivalent of the Huns or Mongols sweeping north into central Asia?