We analyze whether and how iron technology drove political consolidation in pre-imperial China (770–221 BCE) using the China Archaeological Database (CADB)—689,943 grave goods from 98,020 sites. Dividing the era into eleven 50-year subperiods, we construct a state-level proxy for its quantity of iron weapons and estimate panel and instrumental-variable models linking lagged iron weaponry to subsequent state outcomes: territorial expansion, and survival. States with greater prior iron-weapon prevalence were more likely to win wars, expand territory, and avoid conquest; the effect of iron technology is robust to controls for agricultural productivity, terrain ruggedness, waterways, population proxies, and iron ore reserves. Based on woodland availability and distance to nomadic threats, the IV exercise confirms the baseline effect of iron technology to be causal. Additionally, we find that bronze weapons and iron farming tools do not consistently have a significant impact on a state’s territorial expansion and survival. In some cases, their effects even show signs opposite to that of iron weapons. Therefore, persisting with old technology or applying new innovations in non-battlefield contexts did not necessarily enhance a state’s offensive or defensive capacity. Mechanism tests show that resource-mobilization and other state-capacity challenges posed by iron weaponry stimulated state building—policy reforms, county formation, and broader elite recruitment, which set the rival states apart and led to the eventual outcome of the Qin winning to form the first empire.