2. In a free trade area, barriers to trade among member countries are removed, but each country determines its own external trade policy. In a customs union, internal barriers to trade are removed, and a common external trade policy is adopted. A common market is similar to a customs union, except that a common market also allows factors of production to move freely among countries. An economic union involves even closer integration, including the establishment of a common currency and the harmonization of tax rates. A political union is the logical culmination of attempts to achieve ever-closer economic integration.