First actual post. I did some research. Hopefully, I'll go into some deeper issues later. Have suggestions? Comment below!
Back in Song Dynasty (11th~13th Century), we (Oh yeah, I'm a Chinese) had the highest GDP in the world (Even if it's guesstimated. Source: The World Economy: A Millennial Perspective by Angus Maddison), with a per capita GDP of $450~$600, higher than anyone else in the world. Lots of foreign trades, lots of cities, and we even invented paper money!
And then Mongolians invaded us (Yuan Dynasty). High GDP is gone. Why?
1. We are sedentary, they are nomadic
While all these peoples (They're not considered as a part of Han people) was roaming on the land, we don't. We build permanent houses to settle. We farm around where we live. They live in Gers which can be dismantled and moved easily. They hunt stuff. So, they are stronger as they move a damn lot.
2. We have a lot of civil servants, not military
Tax, money-printing, foreign trade management...At that time the government cares about the economy. And, since Song dynasty was built from military coups (Almost ALL OTHER DYNASTIES are built from either invasion or revolution/civil war. Excluding Tang.), they know that the way to prevent another coup against themselves is to have less power in these military officers' hands. And we're just dumb at warfare. In Song Dynasty, there's war every day on the northern border.
3. We are not innovative (But they're not, either.)
Sheng Kuo discovered oil. In his Dream Pool Essays, he said the locals burn this and it has a very thick black smoke, but he used it as an ink, saying oil will be popular for writing, because "Trees (Before we use trees) will be gone, but this thing will never be gone". Today, you probably will say "Such a dumbass guy". We also discovered some uses of gunpowder, but it is mostly used in fireworks, not like military stuff.