At Discover I have a long review up of Empires and Barbarians: The Fall of Rome and the Birth of Europe. I would recommend the book, especially if you enjoyed The Horse, the Wheel, and Language or Empires of the Silk Road. In any case, I want to highlight two points in the author’s argument which I think bear more emphasis.
First, the author argues that there was a mass migration of German (and others, such as the Iranian Alans) across the limes as the Western Roman Empire collapsed in the 5th century. This is in contrast with the model that the barbarian war bands were of trivial size, and most cultural and social evolution occurred through a process of bottom-up emulation. In this model the Ostrogothic elite of Theodoric’s time was a motley ad hoc construction of recent generations whose origins were diverse, German and non-German, without much time depth. Against this model is that of total replacement, which was common in the early 20th century. Empires and Barbarians takes a reasonable middle road; in very few regions was there total replacement, even in what became England where cultural obliteration of the Romano-British heritage was nearly total. But, the author also argues that the core of groups such as the Goths and Vandals were German tribes which had relocated from Central Europe, and whose identities were deep and to a great extent ethnically demarcated. Additionally, not only was this movement of some size, it also included women and children, and so was a classic Völkerwanderung.
But just as there was no total replacement of Romans in northern Gaul, despite the non-trivial influx of Franks into that region, so the migration out of Central Europe did not leave the old Gothic or Vandal heartlands empty. In fact, the majority of those German tribes and clans which identified as Goth or Vandal may have remained in the heartlands. But critically the elites, and in particular the ruling houses and the free warriors and their families decamped. Roughly the top 10-20% of the population.
This is not so surprising. If you read Albion’s Seed: Four British Folkways in America you observe the importance of “forward elements” in British migration to the United States. In Puritan New England there was a proactive attempt to discourage the emigration of the lower classes (as well as the blooded nobility), and a strong bias toward the “upper middle class” (the professions, the gentry, etc.). In the lowland South nobility of England often brought their own hierarchical social system along with them, including their customary retainers. It took some wherewithal to move en masse in an organized fashion. But the author also points out that in the ancient world there was little motive for peasants to move, as there was little difference in quality of life from locale to locale. In a world where productivity gains were marginal and zero-sum economic psychology dominated the motive existed for the rent-seeking elites to move onto greener pastures, not the productive peasantry who were the green pastures no matter where they were resident.
A class dimension to the Völkerwanderung is something that I think might be important, because I recall reading archaeologists noting how robust and tall the Lombards who entered Italy in the 6th and 7th centuries were on average. In the work I had read this was interpreted naturally as an ethnic difference, as the Germans were a larger folk than the local proto-Italians. But if there was this class bias in migration then the size difference has a more natural explanation: the malnourished majority of the German population never emigrated, rather, it was the hale and robust warrior elite who show up in post-Roman states. But there’s a bigger issue here, and that’s the point that pre-modern elites viewed wealth through their own lenses as rentier thugs. In The Fall of Rome: And the End of Civilization Bryan Ward-Perkins emphasizes that the collapse of the Roman Empire did result in a social and economic regress. The data from Britain for example shows that air pollution because of industrial economic activity (broadly construed) did not reach the levels of the Roman period until the 18th century! In Empires and Barbarians the author also agrees that the Roman Empire was wealthier than the barbarian lands to their north and east, and in particular that the German dominated Jastrow and post-Jastrow societies practiced an extensive form of low productivity (per unit of land) agriculture which made their conquest economically a losing proposition for the Roman Empire. And naturally the relatively low per unit economic productivity of the German heartland resulted in fewer rents for its local elite.
And yet set against this we have the arguments in works such as A Farewell to Alms which assume as a default model that the median human in all societies from the emergence of humanity until 1800 was poor. Caught in the “Malthusian trap,” whereby gains in productivity were always swallowed up by population increase. This perspective gains some support from Contours of the World Economy 1-2030 AD. Before 1800 the differences in median wealth across regions is marginal, with the largest gaps being 50%, and 10-20% more typical. From our modern perspective everyone was caught in the Malthusian trap, on average, though some were marginally more well off than others.
But it isn’t the average difference which matters, it is the aggregate whereby you calculate total wealth in a political order. By that measure, even if the Roman peasant was no more well off (or even less well off!) than the average peasant on the Baltic, the high population density of the Roman political order was extremely beneficial to any rentier elite seeking to capture or extract surplus productivity from these teeming masses. In a pre-modern political order poverty may have been a permanent feature of the lives of most, but the configuration and implementation of subsistence and the distribution and flow of goods above subsistence were of the essence. It is much easier for men with swords to steal from densely settled agriculturalists than nomads or slash & burn cultivators. The Roman peasant may not have been wealthier than the German peasant, but the Roman aristocrat of the 4th century lived a life of glamorous opulence in relation to the German warlord. Similarly, the Chinese peasant may not have been wealthier than the cultivators who lived beyond the frontier in 16th century Manchuria, but the Manchu dynasty fell into orders of magnitude more wealth after they toppled the Ming because they captured the much richer flow of rents.
The narrative of Empires and Barbarians is much denser than the above, and the analytical framework more sophisticated. But I think it is critical to emphasize why ancient barbarian elites were so keen on conquering civilized states, and why there seems to have been less mass migration of the peasantry. In the modern world when we think of differences between societies in regards to wealth, complexity or glory, we consider the median man on the street. This would tell us little for most of human history, rather, we would have to focus on the top 10% to truly get a sense of the difference, and in particular the top 1%. To a great extent civilization has been a racket which operates to the benefit of the tiny elite by making rent-seeking much more efficient.