A land-locked republic in South America, Bolivia was part of the Inca empire during the 13th-16th centuries. It was conquered by Spain in the 1530s and, as the Presidency of Charcas, was attached to the viceroyalty of Rio de la Plata. Notable primarily for its rich silver mines, which were exploited and depleted by the Spanish, Bolivia was an imperial backwater for three centuries. In 1825, the Spanish were expelled, and Bolivia, taking its name from the Great Liberator Simon Bolivar, became independent. Bolivia has been beset by numerous wars and revolutions. In the first 100 years of its independence, Bolivia lost territory to Chile, Brazil and Paraguay, three of its four neighbors. Its only coastal territory was lost to Chile in the War of the Pacific (1879-84). Chronic internal instability has given Bolivia one of the lowest standards of living in Latin America. Its government has been a bewildering succession of military dictatorships. In recent years, anti-American feeling has grown because of the government's efforts, under U.S. pressure, to limit the traffic in coca, the raw material for cocaine. Because of frequent shortages of regular postal issues, revenues, postage dues and bisects frequently are used provisionally by Bolivian post offices.