Pursuing other leads altogether today, I chanced upon the comment that the Ottomans before 1444 rather easily asserted dominance over Albanian tribes and families because those were too busy warring with each other to fight off the invaders. Each hoped to use some alliance with outsiders to their advantage against their purely local competitors.
This is a far more common history than tribes unifying to fight off a common enemy. All those sci-fi movies about every nation on earth working together to fight off invading Martians and such? Those were American movies. Other countries don't think like that. Tribes have to reach a certainly level of impulse control and self-observation before they can even consider such unity. Germany was not a unified country for most of the 19th C, and nationalistic movements did not gather steam in general until the American Revolution proved that it just might work. Nations are a late development. Empire, separate nations being made to work together, is the older form. It works great until it falls apart, at which point it gets bloody. Simpler, though. It relies less on humans generally making sense and more on a few humans making sense.
It causes us to misread history. Native Americans did not perceive a Europeans-versus-Indians conflict, but a more complicated equation of seeking alliances with the better European tribes to gain advantage for their tribe against other native tribes. Yeah, we really prefer the white-guys-genocidally-eliminating-red-guys narrative now, because of how much life sucks for Native Americans, but it just isn't true. Similarly, once Crusaders made it to the Holy Land, they discovered that Muslims were not all alike, and Muslims treated these new European Christians as potential counterweights in their own battles with other Muslims. They emphatically did not regard the arrival of Frenchmen and Italians as a hegemonic invasion by Europeans, or see them as automatic allies of the Christians in Constantinople, but one more puzzle-piece in the jockeying for position for power in Antioch and Syria, Jerusalem being somewhat secondary.
Afghanistan is impossible to conquer because the tribes cannot ally. That seems backward, but it is true. Yet what good does it doe them? They remain incredibly poor, except for the few. Ha ha you stupid British/Russians/Americans. Guess we showed you, huh?
We don't see it that way now. We retrospectively apply the distinctions we think they should have applied: Albanians vs Ottomans, Natives vs Europeans, Muslims vs Christians. Those fit our current politics. They have little to do with how people saw the conflicts then.
We see this on an even more micro level. Icelandic males did not see the competition from American servicemen coming, and kept their focus on outdoing each other. (The stereotype is that females pick up on the threat from the arrival of exotic females much more quickly. I don't know if that's true, though.) White supremacists worked hard to keep black people down while Jews and Asians came in and ate their lunch in the job market.
Working together is the exception.