A common AH trope is the idea of the Roman Empire becoming another China by being united for many more centuries or, conversely, China being split up for long periods of time like Europe and the Middle East.
Well, to expand on this idea, what are some other possible "Chinas" and by that, I mean:
- A very large area with a common culture and language; which would have 600 million to 1 billion people at minimum by the modern day.
- An area that perceives itself as representing a continuous nation and civilization, recording and studying its own history precisely even in the pre-industrial era, and identifying with the inhabitants of its own area hundreds of years in the past. (e.g. Huaxia)
A few obvious candidates would be the Roman Empire of course. India, possibly united since the Maurya period. Or Persia--although it would have to derive from the Sassanid period and its "proto-nationalist" impulses and idea of Eranshahr, rather than the universalist Achaemenid period (which would probably not assimilate large areas of land).
Some more uncommon candidates that I would suggest:
- Persistent Frankish empire (The pre-Carolingian, shortly post-Carolingian, and also Napoleonic sphere of influence showed that France could indeed hold those areas. Frenchmen and Normans also had influence over very large parts of Europe and Mediterranean throughout the Middle Ages and Renaissance)
- Inca Empire undisturbed is able to conquer the Southern Cone and Colombia, spreading Quechua and the Inca imperial traditions
- A state that unites the entire North European Plain; potentially a Carpathian Mongol horde turned Holy Roman Empire successor; but it could also just be a Hunnic/Germanic/Slavic confederation turned kingdom of kingdoms.
- Egypt-Fertile Crescent empire. Could be Pre-Islamic, could be Islamic. Perhaps a more territorially limited Caliphate at first with more intensive, less widely spread Arab settlement in the Levant and Egypt only, which later expands en masse into East Africa and North Africa. This would also prevent the Turkic mercenary recruitment that created so many of the breakaway dynasties from the Caliphate.