M. Chandler, quite true, apparently New Orlean's has it's fair share of chaos, as does the reservation. But it is directed within the same groups, or it tends to be so. The paradise in which I reside, for example has the highest murder rate in the entire US. But once the border's crossed, it's like a different country (which to a point it is).
Excepting for the c. 1840's NYC and the NYC draft riots, Haymarket, the 1877 RR stike and the more recent goings on in LA and Watts, Detroit etc, the US has not seen that much mass violence by the underclasses. But the US did have a release as it were, namely the manifest destiny period (which obviously did the Indians no good). And certainly more stable than the chaos in the late middle ages. But a like situation existed there also, after the development of the wheeled moldshare plow, they did have an equivalent land expansion. And the Crusades sent a fair amount of frustrated people elsewhere-even by following idiots like Peter the Hermit. (Bohemond's behavior during the crusades, being a good example of this condition amongst the upper classes, Guiscard had excluded him from primogeniture) I'd wonder how much the underclass revolts of the 1300's and 1400's on..had their roots in the earlier period. But then, plague, gunpowder, and the printing press played a obvious role.
And probably your quite right, insofar as these events quell out when the lower orders lose their martial traditions or rights. Probably amongst the reasons England had fairly few of these events, as compared to France, in the late Gothic. But then again, sending your yeomanry over to loot a few French towns probably defused some of the aggression...or sent it elsewhere anyway.
Ironically, we don't quite have a modern equivalent interest to the period interestin the fechtbuchs. ( many of the gun rags are more fantasy than useable tactics) When the fechtbuchs were printed, amongst the primary users were guilds, trader caravans and others not traditionally amongst the armour plated entitled. We seem to be going the reverse direction, as any learning which incorporates potential violence (or the discipline to use it, or not) is viewed as a virtual social disease.

