Since 1934 the United States has attempted to maintain “most-favored nation” treatment as an organizing principle for world trade. This principle, which requires that countries preserve a unitary external tariff for the same goods imported from different countries, has been given legal status under domestic statutes and the General Agreement on Tariffs and Trade (GATT). Since the formation of the European Economic Community (ECC) or Common Market in 1958, however, a major challenge has been posed for the most-favored nation principle. The EEC has gone outside the six original Common Market countries to conclude a number of association agreements, generally with less-developed countries, in which the parties set tariff levels on particular goods at a rate lower than those set for the rest of the world.