What explains the huge population of Asia throughout history?
I could be as funny/silly, and say “the kamasutra”? Seriously, though, probably, but I’m no expert, the population of Asia in ancient times found itself in a temperate/subtropical climate, and thus thrived, that I suppose could be one reason. Extreme heat and extreme cold do not allow for great population increases, while a great deal of Asia is spread across the tropical areas. But if I’m wrong, why don’t you look up demographics in a good encyclopedia? Anyway, getting to Asia from Africa was so long ago we have no idea how many people made it, long before even the oldest pre Christian religions!