Of course, that we speak of "the British" is a testament to a certain level of success of melding English/Scottish/Welsh identities, much of which happened in the context of imperial endeavor. And certainly many other groups (Sepoys, say) found their interests aligned at times with the imperial project, in a way that outweighed their ethnic background.
Being open to a flexible interpretation of identity/citzenship (Brits, Romans) or having a nominally universal ideology/religion (Americans, Islamic caliphates) seems like it be a large help in successful world leadership, even if it's not a prerequisite.
I find this interesting, because Chinese identity, as much as it is tied to Han ethnicity, seems to be something that could include once-outsiders, as long as they assimilate into it. The OP itself cites how the Mongol invaders established the Yuan dynasty, and the Manchu did the same with the Qing. Despite there is always a separation between Han and non-Han, I've found that the traditional (pre-20th century?) idea of "Chinese" is more tied to cultural traditions and the Confucian ethos, than ethnic/racial divisions. In some ways it's almost comparable to the concept of being "American" as in from the U.S., though of course far less malleable and open to including outside traditions.
"3000 years before the Han dynasty, when what we call China today was inhabited by various tribes, the mythical ancestors of the Han, the Huaxia, controlled swathes of land centered around the Yellow River. According to legend, the leader of the Huaxia, Huangdi, defeated the 4 surrounding tribes, to the North, South, East, and West of Huaxia and incorporated their people and territory. The 4 leaders of those tribes, along with Huangdi became known as the 5 Emperors. Legends also tell of Huangdi defeating and assimilate the tribe of Yandi. Together, Huangdi and Yandi have been viewed as the progenitors of the Han race, which refers to itself as 'descendants of yan and huang'."
Even from the beginning, the Chinese came from the intermingling of multiple peoples, not one specific race. So I think the identity of "Chinese" can certainly be more cultural than ethnic/racial, and so open to outsiders who self-assimilate.
The questions are, what is Chinese culture in modernity? And if traditionalist Confucianism makes some sort of comeback, how will the world outside China react to it?
Oh, and how do current Western/non-Chinese expats in China assimilate to local Confucian norms?
Granted. My own personal take is that you need to be very aware of the substrate (which includes genetics, ethnicity, religion, geography, available resources, etc.) and have a vision that is greater than the substrate. The problem with American empire at the present moment, in my very strongly held opinion, is that we are denying the impact of the substrate and launching into "economic-magic" which is very detached from value of any kind -- with the strong risk of impaling not only our own traditional strengths (goodbye American car companies) but the rest of the world economy with it.
Along these lines, I wish the Chinese all the best for producing things things well that we care about and buy -- this is esp. true of Taiwan, which has retained some measure of traditional positive values that are not entirely materialistic, and I have some optimism that the not longer particularly Communist part can develop in a not especially materialistic direction.
From the outside. On the inside, I think most Britons identify more as English, Scottish, or Welsh than British. Scotland and Wales live under the semi-official delusion that they are actually "countries" in some meaningful way, not just autonomous subdivisions of the UK, and even compete separately in international sporting events outside of the Olympics. Even forming a unified soccer team for the Olympics that the UK itself is hosting was a source of significant controversy.
The controversy mostly stemmed from the potential effects of running a British football team, particularly regarding the UK's status within FIFA.
The home nations each have a representative within FIFA, UEFA and IFAB, as well as being able to compete individually, and collectively enter more club teams into the UEFA Champions League. This causes some tension with other countries, who see the UK as a single country that wields undue influence in the global game.
If the UK establishes its own football team for the purposes of the Olympics, then there is a fear that FIFA would use this as an excuse to shut down the Scottish, Welsh and Northern Irish FAs and force them to fold into the FA. This is the reason Scotland refused to allow its players to be picked for the Olympics.
The Scottish FA never had the power to "refuse to allow" anything, there just weren't any Scottish players worth calling up. The Welsh FA made the same statements but that didn't stop Welsh players from being called up.
Britain's status in FIFA demonstrates just how poorly the notion of a "British" national identity has taken hold.
Being open to a flexible interpretation of identity/citzenship (Brits, Romans) or having a nominally universal ideology/religion (Americans, Islamic caliphates) seems like it be a large help in successful world leadership, even if it's not a prerequisite.