Shannon Love does not believe that most ancient empires resulted from “the unusually aggressive nature of their parent-societies,” which then “swept over their more pacific neighbors.”
If anything, they were, if only initially, Egalitarian Empires, which benefited from a larger manpower pool, merit promotion, and easy assimilation of conquered peoples:
Genghis Khan welded the martially skilled but fractious Mongol tribes into history’s most proficient military. Prior to Genghis, every individual lived in a deeply hierarchical society where birth dictated station. Even the clans themselves existed in hierarchies. Occasionally, a militarily successful Khan would collect an army of follower clans but those armies were poorly disciplined and tended to evaporate at the first major reverse. Genghis disrupted this system by ruthlessly promoting strictly based on merit. He even killed his best friend and oldest ally in a quarrel over the practice. Not only did this improve the quality of leadership but it secured ironclad loyalty from those whose new position in life depended entirely on the continued rule of Genghis. Later he treated non-Mongols, such a Chinese and Arabic engineers with the same evenhandedness. He conquered nearly twenty-five percent of Eurasia in his own life.Unfortunately, Genghis Khan broke his own rule when choosing his succession. He divided the empire among his sons and grandsons, many of whom could not handle the responsibility. The tradition of merit promotion disappeared and the Mongol Empire fractured and dissolved into the conquered cultures.
The Roman Empire’s life cycle divides neatly between the Republic and the Empire. The two labels apply not only to the form of government in each era but also the Empire’s egalitarian, expansionist phase and its inegalitarian, declining phase. The Republic seems to have arisen when the monarchy lost a series of wars and the nobility turned to the plebes in desperation. The plebes demanded representation and the Republic followed rapidly. Just by looking at the map one might think that the Republic conquered far less than the Empire but, proportionally, the Republic went much further. Moreover, the Republic fought against peer societies, opponents with similar technology, knowledge and population density. The Empire, by contrast won its victories largely against primitive societies with much smaller population densities. It failed to make any headway against the Persians, who more evenly matched the Empire in terms of population density and technology.
When the Republic devolved into the Empire, the Empire’s power-density began its long slide. The Empire struggled to field armies one-half of the size of those of the Republic, even though it possessed a much larger population to draw on. Neither could the Empire match the training and motivation of the armies of the Republic. The armies of the Empire increasingly became composed of mercenaries with no willingness to fight the pitched battles in which the armies of the Republic regularly engaged. In the end, Roman armies could fight no better than their “barbarian” opponents. Indeed, the armies of the late empire were usually nothing but ad hoc assemblies of “barbarian” mercenaries.