system
Given the following post, respond as if you're commenting on Reddit:
human
Why did/do East & South Asian nations have such higher population density? 

 Is it that rice cultivation was that much more calorie producing per acre compared with the staples of other parts of the world of the time or...?  

Just curious - rice is a staple = high population density, seems to be a correlation, and I'm thinking it's a causation. Not my field though.  Actually, I don't know exactly what field such a question belongs in.
gpt
Water is in general the answer. If you look at a population map for any human populations, they will be highly clustered around available water sources. Look at a density map of India, it will be concentrated in the front of the Himalayas. Why? Because the mountain range 'captures' the monsoons and funnels them down into the flood-lands bellow. That area has an absolutely ungodly amount of water available. The other areas of high density are in Bangladesh, which in many ways functions as essentially a delta for the Ganges. So, mostly water. Those places also have the advantage of being largely flat, which makes it easy for people to live and helps retain soil quality, and they tend to have very long growing seasons. Humans ain't that special, they live on the same restrictions as other organisms. The population maximum will largely be determined by how much food is available for the population. Modern technology may expand how much we can produce and where we can send it, but it does not essentially change the calculation.