Depends on how deep you want to go, in terms of how far back you want to go. Some elements you could see the centralization of China as deriving from are:
- The capacity of the Yellow and Yangtze Rivers to raise large and dense populations allows polities to form early there and then to dominate areas towards the south.
- The sharp transition between the steppe and very productive agricultural land is unusual in world geography; the North Chinese plain is both very invadable and very able to organise armies under civilization to oppose invasion, and so you'll see militarization at the northern margins of this territory that will tend to reinforce the advantages of the north towards the south in political domination.
- Once political domination is secured, large and dense populations in the river basins also tend to overflow demographically and spread the shared language and culture to the south, along with actual movements of people and kin ties, and these people will then all tend to see themselves as a single people and tend towards a single polity. Again this will be reinforced by conflict with steppe groups which reinforces the "Us Against Them" dynamic.
- Relative isolation from other centres of civilization in Eurasia and distinct traditions, reinforces the idea of a single people with a shared tradition.
- The nature of writing, which will tend to inhibit formation of distinctive linguistic identities.
It's hard to see how any of these can be weakened a lot, but if you somehow weaken all of these a little bit, you might be able to do something? Different writing with a more phonological base, greater influence of Buddhism or Islam in the south and/or west in splitting off a culture as consciously separate, random chance events leading to a weaker set of groups on the northern steppe with less capacity to galvanize China, a less stable settlement of the early Warring States with less of a clear winner that can then colonize out. All relatively small things that could add up to a lot without being an unrecognizable world.