For what it's worth, one theory seems to be that unity itself causes stagnation. Or rather: that division and competition urge on change and innovation. That theory is outlined in the recent book that is talked about
in this article, for instance. The author, Joel Mokyr, argues that political and institutional circumstances, by themselves, are at least just as important as cultural factors: "
People have given different answers, and I’m giving mine. One way of thinking about it is culture. But to state, “Hey, the Chinese have a different culture because they were Confucianists, and the Europeans were Christian,” I don’t buy that for a second."
I actually don't agree with his view entirely; I don't think he's giving enough credit to the importance of cultural attitude. Although that's partly (it seems to me) because he is trying to get his own point about the importance of political and institutional circumstances across. His ultimate conclusion is that cultural attitudes and political and institutional circumstances both influence all of this, and are interrelated. Later on in the article he mentions (implicitly) how important general attitudes can be (although his statement is necessarily a simplification): "
China wanted stability and security, and they achieved that for a long time. The Europeans don’t want stability. They want progress."
The way I see it, cultural attitudes influence the political and institutional situations, so having different cultural attitudes can be an impetus to have a different situation, politically and institutionally.
But at the same time (and this is Mokyr's main thesis), the political and institutional citcumstances
also shape the cultural attitudes!
...so perhaps it isn't even needed to seek out a POD that hinges on a different philosophical/religious paradigm. Merely coming up with a POD that keeps China politically divided would likely lead to changes in the cultural attitudes. Specifically: the competition between various states would cause "stability" to be valued less, and "innovation" to be valued more.