A dearth of free citizens who were willing to fight for their own freedom and the values of their civilization

From Carnage and Culture by Victor Davis Hanson. Page 156.

Franks, Lombards, Goths, and Vandals may have been tribal, and their armies were poorly organized; yet such “barbarians” nevertheless shared a general idea that as freemen of their community they were obligated to fight — and free to profit from the booty of their enemies. In that sense of civic militarism, they were more reminiscent of the old classical armies of a republican past than had been the hired imperial legionaries on Rome’s defensive frontier:

The massive reliance on citizen-soldiers in the West lowered the demands on the central government for expenditures to support the military. . . . Indeed, the flexibility of the West in building on developments that took place during the later Roman Empire resulted in immense military strengths, which, for example, proved their worth in the success for two centuries of the crusader states against overwhelming odds. (B. Bachrach, “Early Medieval Europe,” in K. Raaflaub and N. Rosenstein, eds., War and Society in the Ancient and Medieval Worlds, 294)

The legions had crumbled not because of organizational weaknesses, technological backwardness, or even problems of command and discipline, but because of the dearth of free citizens who were willing to fight for their own freedom and the values of their civilization. Such spirited warriors the barbarians had, and when they absorbed the blueprint of Roman militarism, a number of effective local Western armies arose—as the Muslims learned at Poitiers.