Trade integration within Europe has also benefited peace and security. The view that international trade can reduce the risk of war goes back to Montesquieu and Kant, and has spurred a large empirical literature. Multilateral openness (or “globalization”) does not reduce the risk of war between pairs of countries. However, bilateral trade, by increasing the opportunity cost of conflicts between two partners, reduces the probability of conflict between that pair of countries (Martin, Mayer and Thoenig 2008), even when controlling for historical, linguistic and cultural similarities between populations (Spolaore and Wacziarg 2012). In fact, Martin, Mayer and Thoenig (2010) find that country pairs with a high frequency of old wars are more likely to sign regional trade agreements, which can be explained as a consequence of the complementarity between economic and political gains from trade. They also show that multilateral trade openness, by reducing the opportunity cost of a bilateral conflict, increases the political incentive to sign regional agreements for security reasons.