When discussing China and its history in popular parlance, the term "Han" is thrown around so often that it seems to be a pre-supposed axiom. But surely this was not always the case?
China is rather big, and the "Han" cover an absolutely vast area, and essentially all of "China proper." Today, "Han" is of course the prevailing ethnic identity across this whole territory, but is projecting such a notion of homogeneity onto pre-modern China appropriate? There are for example, numerous subdivisions such as the Hakka, Min, Cantonese and Wu peoples, each with tens of millions of people belonging to them. Do these groups descend from ethnicities that were once seen as separate from the Han, or is the very notion of the "Han people" an abstraction?
In any case, when does this idea of the Han Chinese, and China as a political entity based around Han ethnicity and culture, emerge in Chinese history?
The jury is still kind of out. My familiarity is admittedly more with Manchu than Han identity so I can't give as in-depth an explanation as I'd like, and hopefully someone with greater familiarity with the Ming and/or Republican periods can fill those gaps or indeed supersede me outright. But there is a strong argument for saying that it was under the Qing that 'Han' morphed from a cultural to an ethnic identity, albeit in a somewhat fragmented process across a number of contexts.
'Han' as a cultural marker, denoting participation in a lifestyle revolving around sedentary agriculture and following a broad set of religious and spiritual practices, dates back to, well, the Han Dynasty, from which the term derives its name. But the emergence of a concept of 'Han' as ethnicity goes much, much later. This past answer of mine goes into that.
Please do ask if you or anyone else reading this has follow-ups.