I took a class on "Revolution in the 20th Century" as an undergrad, and the professor there pointed out that Chinese agriculture is built on marginally-fertile

I took a class on "Revolution in the 20th Century" as an undergrad, and the professor there pointed out that Chinese agriculture is built on marginally-fertile land; they absolutely depend on large irrigation networks and on using human waste from the cities to fertilize the countryside. And those networks require a large centralized government to maintain them. Which is why China has had large centralized government, of one form or another, for so many centuries (although not continuously).