When technology levels: the cost of arms and wealth inequality in the ancient world

A long tradition in historical sociology holds that broad military participation makes societies more egalitarian, but the idea is hard to test. This paper uses a global archaeological database of settlement-level wealth Gini coefficients (Bogaard et al. 2025) to test a version of the Andreski (1954) hypothesis: that iron, a cheap, abundant, and mass-producible metal, lowered inequality by broadening who could be armed, while bronze, an expensive and elite-controlled metal alloy, favored the concentration of wealth by keeping the means of violence tightly controlled. In the Eurasian ancient world, where both metals were indigenous, three econometric designs support the “democratization of violence” thesis. First, within the same locality and holding the appropriability of agricultural production constant, iron is associated with a Gini of wealth about 0.07–0.10 lower, while bronze carries no association. Second, an event study around iron’s local adoption shows a similar effect. Third, in a spectrum of technologies, iron is the only one that reduces inequality: bronze, the plow and animal traction, cavalry, and writing are all null, as the cost structure of technology predicts. The estimates are robust to plausible error in the coded adoption dates. The findings are exploratory and concentrated in the Iron Age Mediterranean and Britain.