system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did the Chinese succeed in reaching a higher population BCE and continued thriving for such a longer period than Mesopotamia?

were there any factors like food or cultural organization, which led to them having a sustained increase in population?
gpt
You might be familiar with how the Nile River in Egypt works from school.  If you aren't - for 9 months out of the year the Nile has a moderate flow rate that is sufficient to support human settlement and agriculture.  For the remaining 3 months the Nile's flow rate increases dramatically and it floods a huge area around its river banks.

That flooding might sound bad but its not.  Using soil for agricultural purposes will deplete it's minerals within about 100 years.  That's a long time compared to a human life, but not compared to a civilization.  When the soil runs out of minerals you can't grow anything in it anymore, and it turns out that this is the limiting factor for most civilizations.  IE, a civilization will begin intensively farming its soil, deplete the soil, then starve to death.

In the modern world we're able to replenish the soil's minerals with fertilizer.  They were sort of able to do this in the ancient world as well, but this involved transporting huge amounts of animal manure which is difficult to do and, in practice, if an ancient civilization had to manually fertilize the soil it would result in very low agricultural yields.

This is what makes the Nile's floods so good for the development of civilization - every time the Nile would flood it deposits a huge amount of new soil in the areas that got flooded.  The source of that new soil was hills and mountains in Central Africa, so it was filled with minerals.  Or to put it another way - every year the Nile naturally dumped a huge amount of fertilizer on Egypt.  

This natural fertilizing allowed Egypt to be by far the most productive agricultural region West of India for thousands of years - everyone from the Pharaohs to Alexander the Great to the Roman Empire fed themselves using the food that the Nile was able to grow.

How does this relate to China?  The Yellow River in China is the same type of river as the Nile.  It spends most of the year with a moderate flow rate, then has massive floods for a few months that deposit a bunch of new soil along its banks.

Where the Yellow River is different from the Nile is in its size.  The Nile is a single, small river with practically no tributaries or lakes.  The Nile's floods only cover a small geographic area located immediately adjacent to it.

The Yellow River, on the other hand, is a massive system with hundreds of tributaries and lakes.  When it floods, it covers almost the entirety of South East China - which is an area thousands of times the size of that covered by the Nile.  

The Yellow River basin has been among for the most productive agricultural areas on Earth for much of human history.  Because the only limiting factor to population size is a region's ability to produce food, this also means that the Yellow River Basin (and by extension, China) has managed to maintain a huge population for the entirety of human history.