I suppose hinduism could spread that far. I mean consider this, Buddhism actually originates from India. Buddha was a Hindu Prince! And yet its all over the far east (and ironically not much in India). So i suppose Hinduism could spread that far too. (Well Islam and Christianity sure spread a lot!)
Btw, I think you are right about the whole area not being in Hindu control at one point in time. The largest Indian kngdom i remember was of Ashoka, and even that din't completely cover all of modern day India+Pakistan (he gave up war right before conquering the south-most tip because he converted to Budhism).
I think Muslims actually ruled all of the south-asian subcontinent at one time. The Mughals
On the western edge, I found some context about various books and papers linking up Hindu migrations into the Horn of Africa, particularly Egypt. Most of what I read about this was offline, so unable to provide additional dope in here.
Here is a write up listing some studies and names of books to consider:
For far eastern links, read about inter-marriages and relationships for a period of over two millennium between Ayodhya(India) and Seoul (South Korea) [1]. A search on the Kim clan and Princess Heo Hwang-ok and the spread of Buddhist/Hindu culture right up to Japanese coastline can be inferred.
This is kind of the spread of Hinduism in South East Asia [2] before convertists of other religions (like Muslims or Christianity) emanated.
Btw, I think you are right about the whole area not being in Hindu control at one point in time. The largest Indian kngdom i remember was of Ashoka, and even that din't completely cover all of modern day India+Pakistan (he gave up war right before conquering the south-most tip because he converted to Budhism).
I think Muslims actually ruled all of the south-asian subcontinent at one time. The Mughals