Author refers to this volume as the "most important" of the series.
Coverage extends from Teutoberg Forest to Tours, though the latter is cursory (for want of reliable source material). Describes the height of the Roman system, its transition and destruction, replacement by a Germanic-Romanic system, its transition and destruction--leading into volume III, regarding the medieval period & feudalism.
Bloody excellent all around. Follows his standard model: chapter text lays out his thesis, with notes, and lengthy excursus for each chapter, where he quibbles with other authorities, i.e., proves that his rivals are dumbasses.
We recall that the central thesis of Volume I was that ancient armies won because they outnumbered the enemy, and that the Romans excelled principally in logistics: getting more guys to the point of crisis than the other side. That system is explained herein as failing because the Roman economy slipped back to a barter system, which destroyed the logistics.
It's good times. Go read now.