I put it very simply here, and I also do not know any specific numbers or facts off the top of my head about this subject. but I'm wondering what are the main historical reasons behind their massive population? Obviously they have the largest land mass, but relative to other countries China is much higher. Why is this?

On a similar note, indias population density is extremely high. Has this been this way historically over time? Have theses regions / areas always had high populations?

Does it have to do with resources? Cultural familial practices? Government policies?

Thanks in advance reddit!