Bring on the demolition crew! (Wright)

So thank heavens for barbarians! If dominant civilizations are stagnant and decaying, contributing little if anything to the march of non-zero-sumness, it is just as well (from cultural evolution's standpoint) to have troublemakers nearby. Better to tear the system down and start over. And because barbarians turn out to be so partial to civilized memes, you don't have to start from scratch!

The barbarian role of cultural demolition crew is especially important when you consider how often cultural reconstruction is needed. Many of Rome's glaring defects—exploitation, authoritarianism, corrupt self-aggrandizement—flow from deeply human tendencies. Time and again they've transformed promising civilizations into decaying, oppressive monstrosities. Time and again, history seems to cry out: Bring on the demolition crew! And time and again barbarians cheerfully respond to the call.

Robert Wright, Nonzero: The Logic of Human Destiny