> I vaguely know that China contains a bunch of peoples and languages, regions with distinct cultures. But very little beyond that.

I know this is fairly off topic but I found Prisoners of Geography [1] a very accessible introduction to geopolitics. (Of course it only represents one point of view, so looking at some other sources would be advisable.) It has one chapter for each large country or continent, including one for China. I'm tempted to put a one-sentence summary of that chapter here based on my half-remembered interpretation of it, but I think that would do more harm than good!

[1] https://www.amazon.co.uk/Prisoners-Geography-Everything-Glob...

To substantiate your point - that's also what I read (specifically regarding sub-saharan Africa). South Africa is the only exception due to it being much more elevated.

Source: https://www.amazon.co.uk/Prisoners-Geography-Everything-Glob...

https://www.amazon.com/Prisoners-Geography-Everything-Global...