Building on economic norms theory, I argue that the causes of international conflict may be contextual rather than constant over time. I explore the temporal patterns in the predictors of conflict in data on European conflict between 1870 and 2001, using an endogenous Markov chain Monte Carlo Poisson change-point model. I find that the period can be divided into two time periods, different in terms of the direction of the effect of the main conflict predictors. While democracy has a positive effect on conflict in the period between 1870 and 1938, it has a negative effect from 1938 to 2001. Likewise, trade initially has no impact on conflict, but later exerts a pacifying effect. Post-estimation analyses suggest that such patterns are best explained by the externalization of contractual norms, which is consistent with economic norms theory.