The Manchurians from...

Manchu.

The Manchurians formed the Qing dynasty. One of the most recognizable and probably the last dynasty before "modern 19th century China." 

The Manchurians thrived, almost doubling the population of the Chinese. However, this same civic pride that the Manchurians had for their accomplishments would soon drive them into a plateau that they could not come out of. The Manchurians had found a way to double food production, following the increase in food production, naturally the population increased due to the abundance of resources.

The Manchurians were a proud people and did not allow intermarriage with the Han Chinese, in order to maintain their bloodline. This pride grew with their success with their success as the Qing and their pride grew in tandem. They believed they were the best civilization in the world and that no one could top them. Not visiting embassies from the west, nor any other culture that came into contact with them to trade or offer their wares.

This pride hurt them. As the population grew their food production slowed. It plateaued as the population growth swelled. When they finally met at their top of production the population stagnated and eventually their food cultivation only allowed for meager portions of food. This created a poor economy, banditry and like all other dynasties this lead to rebellions.