For my alternate history, I am looking for candidates for a polity that would last as one (mostly) continuous entity from the classical age (beginning around 100 BCE at the latest) to the digital age of the 21st century. In OTL, the only such polity is China. Even though China also had periods of division that sometimes lasted several centuries, there is a sense of continuity about the Chinese civilization and the Chinese state starting BCE and going all the way to the present, in a way that is not true for any other polity.
In an ATL, what polity could realistically achieve a similar level of continuity for a similarly long period of time? I am looking for a POD no later than around 100 BCE, but there is no limit about how early it can be - it could be in prehistoric times and thus lead to a completely new, fictional civilization. There can be periods of political division for up to a few centuries, just as in the history of China, but the polity has to be re-united eventually and it has to remain recognisably the same entity in terms of its "character" as a civilization. The biggest possible change in terms of character which I would be willing to accept would be something along the lines of a Roman Empire => Byzantine Empire transition, preferably less.
Here are my thoughts on the matter. I admit to being something of a Jaredian. While I don't believe that geography determines literally everything, geographic factors play an important part in my thinking.
1) India: Aside from China, I view this as the best candidate for the kind of continuous polity I have in mind. In OTL, India is divided among several different language groups and only became one unified polity in modern times, after the British Raj. However, if one civilization with one language somehow manages to dominate most of the Indo-Gangetic Plain early on and continues to do so, I think it is conceivable that India could go a route similar to China.
2) The Middle East: Because of its geography, the Middle East is much harder to unify than China or India. There are several distinct regions where polities could have their center of power - the Nile valley in Egypt, the Euphrates and Tigris in Mesopotamia, Asia Minor, the Iranian plateau... It is unlikely that any one power could hold all these for thousands of years at a time. I find the idea of a lasting Achaemenid or Alexandrian empire intriguing, but I think it would require extraordinary good luck to stay together. The Middle East will also probably suffer more from climate change and desertification through over-use of agricultural land than China or India do.
3) Europe: Also unlikely to be unified for long periods of time. The Romans managed to unite the Mediterranean and some lands beyond it for some five hundred years, but holding it all together for more than two-thousand years is a huge challenge in light of the geographical factors. I wonder, what is the biggest chunk of Europe that could realistically stay together throughout history...
So, what is your opinion? I have listed India as my major candidate, and the Middle East and (parts of) Europe as more unlikely ones who might have an outside chance. Do you agree with my line of thought, or disagree? If so, why? And do you see any other candidates than the ones I have mentioned? Outside Eurasia, the lack of domesticable plants and animals is a major obstacle to creating an advanced civilization. But if anyone wants to try and make a plausible case I have not thought of, I will be glad to listen.