Its been about 8 centuries or so since there have been barbarians hordes that overwhelmed civilization. So, how do we get a modern day (19th century or more recent) barbarian horde that can threaten civilization. Requirements for the barbarian horde are that they are a primarily militaristic and nomadic society that is not out to establish a ordered civilized (urban based) nation (though that can happen eventually, but it can't be their intent). The barbarians must provide a large scale viable threat to one or more major centers of civilization (basicly, the US, EU, or China).
The closest thing we've got in OTL is Al Queda (sic), but they don't quite meet the cut.
The closest thing we've got in OTL is Al Queda (sic), but they don't quite meet the cut.