Do We Still Need Barbarians?

Much of the larger sweep of history can be summed up in a pretty simple dynamic.

When conditions, which are mostly a function of climate, are favorable, civilized settled societies thrive and can keep "barbarians" (historically mostly herders as opposed to more settled farmers) at bay.

When conditions are unfavorable, often again as a function of climate, barbarians rush in and destroy the settled society because their culture is better adapted to adverse environmental conditions, but they either retreat or acclimate to a settled lifestyle as conditions improve again.

Rinse and repeat.

The question then is whether this dialectic is still relevant, or whether we are at "the end of history" at which point the barbarians have grown obsolete.

In a war of competing cultures model, the fierce cultures of honor, globally often Muslim, domestically often Evangelical Christian, have a great deal in common with the barbarians of old. And, we are almost certainly entering an era in which climate conditions will be less favorable for most of humanity.

We would expect a shift in selective fitness in favor of "barbarian cultures" relative to "civilized cultures" as a result.  But, perhaps the technologies which civilized cultures are more suited to nurturing has become so decisive that this overcomes the benefits of cultural norms more naturally suited to a survival/adversity mode.