Topographically the continent is divided into three sections—the South American cordillera, the interior lowlands, and the continental shield. The continental shield, in the east, which is separated into two unequal sections (the Guiana Highlands and the Brazilian Highlands) by the Amazon geosyncline, contains the continent's oldest rocks. Geologic studies in South America have supported the theory of continental drift and have shown that until 135 million years ago South America was joined to Africa; a Brazil-Gabon link has been established on the basis of tectonic matching. Extending down the middle of the continent is a series of lowlands running southward from the llanos of the north, through the selva of the great Amazon basin and the Gran Chaco, to the Pampa of Argentina.

Paralleling the Pacific shore is the great cordillera composed of the Andes ranges and high intermontane valleys and plateaus. The Andes rise to numerous snowcapped peaks; Mt. Aconcagua (22,835 ft/6,960 m) in Argentina is the highest point in the Western Hemisphere. The Andes region is seismically active and prone to earthquakes. Volcanoes are present but mostly inactive. Patagonia, a windy, semiarid plateau region, lies to the E of the Andes in S Argentina. On the Pacific coast, the land between the Andes and the sea widens northward from the islands of S Chile. In N Chile lies the barren Atacama Desert.

There are few good natural harbors along the South American coast. The continent's great river systems empty into the Atlantic Ocean and the Caribbean Sea; from north to south they are the Magdalena, Orinoco, Amazon, and Paraguay-Paraná systems. Only short streams flow into the Pacific Ocean. Excluding Lake Maracaibo, which is actually an arm of the Caribbean Sea, Lake Titicaca, on the Peru-Bolivia border, is the largest of the continent's lakes. South America embraces every climatic zone—tropical rainy, desert, high alpine—and vegetation varies accordingly.

Native peoples constitute a significant portion of the continent's Andean population, especially in Bolivia, Ecuador, Peru, and Paraguay. Elsewhere in South America the population is generally mestizo, although Chile, Argentina, Uruguay, and S Brazil have primarily European populations. There are sizable populations of African descent in NE Brazil, French Guiana, Suriname, Guyana, Venezuela, and Colombia. Immigration since 1800 has brought European, Middle Eastern, and Asian (especially Japanese) peoples to the continent, particularly to Argentina and Brazil.

With the exception of Brazil and Ecuador, the national capitals have the largest populations and are the economic, cultural, and political centers of the countries. Since World War II, the urban population has rapidly expanded. São Paulo, Brazil, whose population is nearly 10,000,000, is the largest city of South America and one of the fastest growing cities of its size in the world. Squatter settlements have multiplied around urban areas as the poor and unskilled flock to the cities; widespread unemployment is common. Outside the cities the population density of the continent is very low, with vast portions of the interior virtually uninhabited; most of the people live within 200 mi (320 km) of the coast.

Beginning in the 17th cent., the exploitation of the continent's resources and the development of its industries were the result of foreign investment and initiative, especially that of Spain, Great Britain, and the United States, but since World War II the nations of South America have sought greater economic independence. An increasing number of South American industrial centers have developed heavy industries to supplement the light industries on which they had previously concentrated.

An early obstacle to industrial growth in South America was the scarcity of coal. The continent has therefore relied on its petroleum reserves, most notably in Venezuela and also in Argentina, Colombia, Chile, Peru, and Ecuador, as a source of fuel. South Americans also have gradually developed their natural-gas reserves; hydroelectric plants produce most of the continent's electricity. Iron-ore deposits are plentiful in the Guiana and Brazilian highlands, and copper is abundant in the central Andes mountain region of Chile and Peru. Other important mineral resources include tin in Bolivia, manganese and gold in Brazil, and bauxite in Guyana and Suriname.

Subsistence farming is widespread, with about 30% of the people working about 15% of the land. Dense forests, steep slopes, and unfavorable climatic conditions, along with crude agricultural methods, limit the amount of cultivable land. Commercial agriculture, especially of the plantation type, fares better in terms of production because of the large scale and the opportunity to use modern, mechanized methods. Among the agricultural exports are coffee, bananas, sugarcane, tobacco, and grains. Meat is also an important export. In the interior, hunting and gathering of forest products are the chief economic activities of the indigenous peoples. Fishing is also a central industry. In the more accessible areas, forest products are removed for export.

European exploration and penetration of South America started at the beginning of the 16th cent. Under the Treaty of Tordesillas, Portugal claimed what is now Brazil, and Spanish claims were established throughout the rest of the continent with the exception of Guyana, Suriname, and French Guiana. An Iberian culture and Roman Catholicism were early New World transplants—as were coffee, sugarcane, and wheat. The subjugation of the indigenous civilizations was a ruthless accompaniment to settlement efforts, particularly those of Spain. The Inca Empire, centered at Cuzco, Peru, was conquered (1531–35) by Francisco Pizarro; other native cultures quickly declined or retreated in the face of conquest, conversion attempts, and subjugation. Spain and Portugal maintained their colonies in South America until the first quarter of the 19th cent., when successful revolutions resulted in the creation of independent states.

The liberated countries generally struggled with political instability, with revolutions and military dictatorships common and economic development hindered. Between 1820 and 1920, the continent received almost 6 million immigrants, nearly all from Europe. Guyana gained independence from Great Britain in 1966 and Suriname from the Netherlands in 1975. French Guiana is an overseas department of France.

Beginning in the 1970s, road building and the clearing of land led to the destruction of large areas of the Amazonian rain forests. International pressure and changes in government policy, especially in Brazil, resulted in a decrease in the deforestation rate since the late 1980s, although burning and illegal logging continue. Efforts to combat the illegal drug trade have been largely ineffective. Peru is one of the world's largest growers of coca leaves, and Colombia is a center for the drug trade.

Economic problems and social inequality have led to considerable unrest and political instability. Many indigenous peoples, angered by centuries of domination by a primarily European-descended upper class, have demanded a more equal distribution of land and power. Despite the increasing industrialization of some countries, notably Brazil, Venezuela, and Argentina, and the widespread introduction of free-market reforms in the 1990s, high inflation and huge foreign debt continued to be major problems for many South American countries. Such economic problems led to a rise in populist political parties and movements in the region in the early 21st cent., most notably in Venezuela and Bolivia.

See also Americas, antiquity and prehistory of the; Natives, South American.