The analysis of Cavalry and Iron is fascinating. As is the correlation between MilTech and Phylogeny (cultural similarity between polities).
I was most surprised that the authors had no strong theories about the role of "agricultural productivity". In addition to building armies from agricultural surplus, the ability to feed horses, people, elephants, etc was key to large military campaign. A common defensive technique against large army campaigns included burning agriculture.. for instance Hannibal's invasion of Rome. ie, the agriculture supply-chain itself seems to be a necessary pre-requisite to military campaigns with thousands of troops.
I was most surprised that the authors had no strong theories about the role of "agricultural productivity". In addition to building armies from agricultural surplus, the ability to feed horses, people, elephants, etc was key to large military campaign. A common defensive technique against large army campaigns included burning agriculture.. for instance Hannibal's invasion of Rome. ie, the agriculture supply-chain itself seems to be a necessary pre-requisite to military campaigns with thousands of troops.