Over the pre-Columbian sequence, Andean warfare ranged greatly in intensity. This review combines published information on cranial trauma and settlement patterns, which often align and clarify each other, to make an initial assessment of how severely Andean populations were affected by war over time and space. The data speak to a number of major topics in the archaeology of warfare, such as the origin of war, contrasts in state militarism, and changes in the practice of war related to social organization. Although there is considerable regional variation, two large-scale “waves” of escalated conflict that are clearly supported by the cranial trauma and settlement pattern data occurred in the Final Formative (late Early Horizon, 400 BC–AD 100) and the Late Intermediate period (AD 1000–1400).