The Yuan follow up on this by being super into global trade, commerce, and cultural exchange (whether anyone else wants to or not)... to the point where their shoddy economic policies, climate change, and the Black Death burn out the Chinese economy and throw the whole region in chaos (again)

Then the Ming comes in, saying "screw that, we're going... See more

This massive economy led to rich trading ties with a large number of its neighbors - including Japan, Korea, and the Indian Ocean marketplace. But the most significant economic ties across the totality of the Song Dynasty would be those not of its own making. Rather, they would be it its competitor and rival states to the north - first the Liao... See more

So, that shifts under the Song policy to a policy of "hey maybe let's not tax the pants off of the peasant farmers, and instead try something craazy." That "crazy" idea is to tax trade - both internal & with foreign entities.

This tremendous growth came about, in significant part, because of a rather revolutionary reform to the taxation policies of the realm.