Free trade is the economic policy that many liberal countries—who are less likely to go to war with each other—have chosen. It’s not the policy that makes them liberal. These studies show such a strong correlation, because the countries that have chosen free trade are largely a huge block of countries that already get along, particularly the EU countries and the US. These countries already have the productive relationships necessary for peace. And history has shown that those relationships can be fostered without resorting to free trade. For example, for many years after World War II, Japan protected many national industries, but it was a peaceful country with a productive relationship with the West. Therefore, the costs of free trade are not necessary to achieve that benefit since it can be fostered under different conditions.  1 Paul W. Kuznets, “An East Asian Model of Economic Development: Japan, Taiwan, and South Korea,” Economic Development and Cultural Change, vol. 35, no. 3 (April 1988)