Economists have, in fact, devoted a lot of effort to documenting how international differences in economic conditions change as national governments lower the barriers that limit trade across countries. Much of international trade theory attempts to imagine what happens when countries allow unrestricted flows of goods and capital across national boundaries. One common theme in these models, which has greatly influenced economic policy, is that the removal of restrictions on such flows increases global income and tends to equalize prices and wages across countries. Decades of experience with various trade liberalization policies, however, do not seem to have had as much of an impact on global income or on international wage inequality as the proponents of free trade would have expected.