the strong, in the famous theory of comparative advantage. In Principles of Political Economy and Taxation Ricardo advanced the doctrine still considered the most counterintuitive in economics: When an inefficient producer sends the merchandise it produces best to a country able to produce it more efficiently, both countries benefit. The ascendancy of free trade was primarily based on national advantage in the mid 19th century. That is, the calculation made was whether it was in any particular country's self-interest to open its borders to imports. John Stuart Mill proved that a country with monopoly pricing power on the international market could manipulate the terms of trade through maintaining tariffs, and that the response to this might be reciprocity in trade policy. Ricardo and others had suggested this earlier. This was taken as evidence against the universal doctrine of free trade, as it was believed that more of the economic surplus of trade would accrue to a country following reciprocal, rather than completely free, trade policies. This was followed within a few years by the infant industry scenario developed by Mill promoting the theory that the government had the duty to protect young industries, although only for a time necessary for them to develop full capacity. This became the policy in many countries attempting to industrialize and out-compete English exporters. Milton Friedman later continued this vein of thought, showing that in a few circumstances tariffs might be beneficial to the host country; but never for the world at large. 20th century The Great Depression was a major economic recession that ran from 1929 to the late 1930s. During this period, there was a great drop in trade and other economic indicators. The lack of free trade was considered by many as a principal cause of the depression causing stagnation and inflation. Only during World War II did the recession end in the United States. Also during the war, in 1944, 44 countries signed the Bretton Woods Agreement, intended to prevent national trade barriers, to avoid depressions. It set up rules and institutions to regulate the international political economy: the International Monetary Fund and the International Bank for Reconstruction and Development (later divided into the World Bank $ Bank for International Settlements). These organizations became operational in 1946 after enough countries ratified the agreement. In 1947, 23 countries agreed to the General Agreement on Tariffs and Trade to promote free trade. The