The Sichuanese might not get along with the Cantonese, but they’re ethnically the same people with a shared culture
One China is a convenient fiction invented by an authoritarian regime, not a day to day reality on the ground.
Westerners buy into it through some combination of propaganda (coming from the Chinese state and our own, both of which benefit from an exaggerated sense of Chinese unity) and our inability to distinguish the various ethnic groups because we're overly fixated on skin color as the primary physical marker of ethnicity.
It's easy to track differences between people around you, in your country, and very hard to track difference between people in other countries. This creates an illusion of "We are very different, and they are all the same".
The 90% Han Chinese number isn't especially useful because it's comparable to the way that most of Europe has historically identified itself as the successor of Rome. That they all identify as Han doesn't make Han a truly useful grouping for judging diversity when they all have different ideas of what "Han" means.
Not at all, these are pretty universally agreed upon by global sociologist.
>Europe is extremely ethnically diverse, as is China
Indeed, Europe is extremely diverse, much more so than China.
>they just don't use skin color as the primary ethnic marker the way that is commonly (and still incorrectly) done in the US.
Neither does the US. Skin color is not a primary ethnic marker. No one versed in sociology in the US considers a Black American ethnically similar to an Eritrean. Nor do they consider a Ukrainian ethnically similar to a White American.
>The 90% Han Chinese number isn't especially useful because it's comparable to the way that most of Europe has historically identified itself as the successor of Rome.
It is extremely useful because the subgroups specifically make these claims: "Modern Han Chinese subgroups, such as the Cantonese, the Hakka, the Henghua, the Hainanese, the Hoklo peoples, the Gan, the Xiang, the Wu-speaking peoples, all claim Han Chinese ancestry pointing to official histories and their own genealogical records to support such claims."
Germanic people do not make the claim to be of Roman or Mediterranean ethnicity nor origin. The languages are vastly more varied in Europe versus China, where 70%+ speak Mandarin.
Additionally, Han Chinese are much closer genetically than Europeans. Italians, Brits, and Estonians have much more varied genetics compared to Han Chinese.
by the standard of most large landmasses, China was, in fact, far more cohesive and united - compared to the hundreds of local lords and kings with their tiny little fiefs in, say, India
Comparing Chinese unity favorably to India is damning with faint praise, and doesn't do anything at all to help your original argument that China has better "social cohesion and political stability" than Western countries by virtue of having less immigration.
We're not comparing the social cohesion of landmasses, we're comparing the social cohesion of states, and India is a particularly disjointed example to use.