Some prominent scholars and public activists contend that a fundamental change in the nature of world politics can be brought about through efforts to change prevailing culture, norms, and ideas. In this view, behavior in anarchy is what the prevailing culture makes of it, since social reality is, in Alexander Wendt's words, “ideas almost all the way down.” Anthropologists studying the causes of war in pre-industrial anarchies have tested this hypothesis extensively. Their research shows that war behavior cannot be reduced to either material factors or culture alone. Rather, material, institutional, and cultural elements must all be taken into account simultaneously in assessing an anarchical society's propensity for war and in designing strategies to promote change. Models of nested causality or of interaction effects between variables can sometimes capture these causal interrelationships, but they cannot capture nonlinear system effects that often play a prominent role. Patterns found in anthropological research can serve as a heuristic for understanding the democratic peace and processes of contemporary international cultural change.