Often what takes place is not so much collapse as reconfiguration -- what some scholars have described as the emergence of a new Middle Ages. And close study suggests that the power of statelets and other new political actors will be less transitory, more significant, and more resistant to intervention than is usually assumed.
What killed off the European Middle Ages was capitalism. In the last decades of the twentieth century, as capitalism began to operate on an increasingly global scale, the nation-state and the other structures and institutions of the modern era started to fray around the edges, leading scholars to talk of a new medievalism.
Wandering through many cities of the developing world today, one comes up against the limits of modernity. Still, although the weakness of the state today is most pronounced in the developing world, the state's retreat is also a global phenomenon. What is emerging is a global economy increasingly centered on what some theorists have called "global cities" -- major urban centers that are connected less to their hinterlands and more to their counterparts elsewhere.
Today, pundits writing about the future of the US empire tend to adopt an inward-looking approach similar to that of earlier generations of historians of the Roman Empire. For example, scholars debate topics such as whether the US economy can bear the cost of maintaining so many overseas military and diplomatic operations. But they tend to neglect the vast portion of humanity kept at bay beyond the empire's borders, who regard it with the same mixture of awe, longing, and bitterness with which the barbarians once regarded the Eternal City.
As states recede and the new medievalism advances, the outside world is destined to move increasingly beyond the control -- and even the understanding -- of the new Rome. The globe's variegated informal and quasi-informal statelike activities will continue to expand, as will the power and reach of those who live by them. The new Romans, like the old, might not enjoy the consequences.