Of poor mestizo background, Simon Patino started as a mining apprentice. By 1924 he owned fifty percent of the national production and controlled the European refining of Bolivian tin.
      Although Patiño lived permanently abroad by the early 1920s, the two other leading tin-mining entrepreneurs (Tin Barons), Carlos Aramayo and Mauricio Hochschild, resided primarily in Bolivia.
      The decline in European tin production also contributed to the Bolivian tin boom at the beginning of the twentieth century. This boom in the tin-mining industry coincided with Liberal Party administrations. The government helped the industry by only lightly taxing the new mining interests and by expanding the country's existing rail system. Although the Liberal Party was overthrown in 1920 by the Republican Union Party, which remained in power for the following fifteen years, there was relatively little change in economic policy. During this period the first important manufacturing industries were established.
      With the development of huge mines in southern Oruro and northern Potosí, La Paz eclipsed Potosí as the mining industry's financial and service center. In the first two decades of the 20th century, Bolivia enjoyed the longest period of peace and progress in its history. The exploitation of tin resources, begun in 1899, made Bolivia one of the world's major tin suppliers. Simón Patiño became one of the world's richest men. British and United States investors became interested in the industry in its early stages, and by the time the mines were expropriated in 1952, a considerable amount of U.S. and British capital was invested in them.
       The 1952 revolution is perhaps the most important political and social event this century and one of the four most important revolutions in Latin America. The government also greatly increased public ownership of industry at the expense of private, especially foreign private, ownership by nationalizing a number of important activities--notably mining, the petroleum industry, telecommunications, and transportation. The new government expropriated the holdings of the major tin mining companies and placed them in the hands of a new state firm, COMIBOL.