If you look at the history of a fragmented region, it appears that the social fragmentation and political disunity is very difficult to reverse or even to surmount. It could be that the very survival of the various isolated groups could depend on them becoming unified, and still they would be unable to overcome their differences despite their own collective self interest. But then at times the conditions do in fact allow for eventual unification into larger and more powerful political units to counteract rival powers and to even become great empires themselves, reacting against previous upheavals, civil wars, and rival wars for conquest, spreading out and expanding and seeking out stability and security before overreaching and falling into decline.
My point here is that there are processes of succession going on here, like succession in a forest. As with a forest, various greater environmental stages - such as the clearing of a space after a fire - allows for certain species to flourish, and then the greater environmental conditions made possible by those flourishing species make it possible for succeeding generations of different species to take hold and so on. It can take quite some time for the right conditions to come about for the right species of trees to flourish and bring about the high top canopy which eventually stabilizes the stages of succession until the next great fire or storm.
I'm not here to naturalize - and thus excuse - the phenomenon of empire, though unfortunately the phenomenon has been with us for thousands of years, and we should cast our weary eyes over the course of history with that realistic assessment in mind. There is a sort of tectonics at work here: a coming and going, with each rising and falling empire influencing each other as they border each other and interact with each other through global trade and war, transforming each other through the circulation and build up of tensions and the eruptions of collisions, heaving oceans of waves and troughs which beget each other.
A couple of them crash and send out shocks, while others rise and butt up against each other. The earth as a finite sphere is eventually filled up with them, coming and going, and so it is the bounded totality that constrains itself to this oscillating fate.
