While the modern theory of international trade allows for many different modeling assumptions, the gains from trade can often be calculated using a common set of statistics. In particular, the share of a country’s output that is consumed domestically, the elasticity of bilateral trade with respect to trade costs, and the relationship between markups and firm size, each have a clear role in the gains from integration. All of these statistics may also be structurally linked to the degree of firm heterogeneity, usually the dispersion in firm-level productivity. Accordingly, the presence of firm heterogeneity may have a meaningful impact on the welfare response to trade liberalization. A quantitative application of a common firm heterogeneity model indicates that increased dispersion of firm-level productivity has a disproportionately large and positive impact on the gains from trade for smaller, less-developed countries.
Long-distance international trade for hundreds of years stemmed primarily from differences in climate. Generally free-trade policy and reduced transport cost superimposed another pattern by 1914; one of greater international specialization based upon land and labor abundance or scarcity. The broadly open trading world of the beginning of 1914 broke down first under the impact of war and then of the Great Depression. By 1945 the United States had emerged as the most powerful nation, committed to establishing a world order that would not make the mistakes of the preceding decades. The promotion of more liberalized trade among the wealthier nations, over the following decades hugely expanded the volume of trade. Trade in manufactures—based on skill endowments and preference diversity—came to dominate that in primary product. Services strongly increased in importance, especially with the rise of e-commerce. Oil displaced coal as the world’s principal fuel, redistributing income to those countries with substantial oil deposits. The greatest threat to the continuing expansion of world incomes and trade came from the Great Recession of 2008–2009, but the World Trade Organization regime discouraged the mutually destructive trade wars of the earlier period. However, the WTO was less successful 10 years later in restraining the damaging United States–China trade conflict.