Under the Treaty of Tordesillas, everything to the east of the line that ran from pole to pole 370 leagues west of the Cape Verde Islands was to be Portugal's to exploit. The exact reason for Portugal's interest in having the line so far to the west is debatable, but the Portuguese may have been trying to keep the Castilians away from the sure route to the East. Very practically, the line's placement gave Portuguese vessels en route to India ample room to pick up winds and currents that took them around the southern end of Africa, a feat carried out by Vasco da Gama on his voyage of 1497-99. The Portuguese also may have known that western lands or islands lay on their side of the line. On the modern map of Brazil, in the north the line cuts across the eastern end of the Ilha de Marajó, and in the south it passes through Laguna on the coast of Santa Catarina. Because most of present-day Brazil lies to the west of the line, clearly the Portuguese expanded successfully on this initial division.

The territorial aggrandizement, which is one of the main themes of Brazilian history, was both accidental and a matter of state policy. Uncertainty as to the detailed geography of South America persisted into the twentieth century, so it is understandable that Portuguese officials professed to believe into the eighteenth century that the estuaries of both the Amazon and the Río de la Plata were on their side of the Tordesillas Line. The two river systems were, in the words of the Jesuit Father Simão de Vasconcellos, "two keys that lock the land of Brazil . . . two giants that defend it and demarcate between us [Portuguese] and Castille." Several centuries of penetration along these river systems gave Brazil its distinctive shape. It could be said that today's Brazil owes its vast territory to the native Indians who served as skilled trackers, warriors, porters, food suppliers, and paddlers for the Portuguese expeditions, and to the Indians whose potential as slaves lured the Portuguese inland.

The Portuguese empire at the outset was a commercial rather than a colonial one. Portugal lacked sufficient population to establish colonies of settlers throughout its maritime empire. The Portuguese practice was to conquer enough space for a trading fort and a surrounding enclave from which to draw on the wealth and resources of the adjacent country. A map of this maritime commercial domain would show a series of dots connected by sealanes rather than continuous stretches of territory. French competition forced the Portuguese shift to colonialism in Brazil. This shift involved the gradual move from trading for brazilwood to cultivating sugarcane, which required control of great expanses of land and increasing numbers of slaves. The first to burst past the Tordesillas Line were the slave hunters. The shift to colonialism was also facilitated by the union of the Spanish and Portuguese crowns between 1580 and 1640. Although the two governments on the Iberian Peninsula and in the Americas were kept separate, trade and travel controls became lax. An active contraband trade developed between Brazilian settlements and Buenos Aires, and Portuguese moving overland appeared in Asunción, Potosí, Lima, and even Quito.

Expansion along the Atlantic coast had been gradual. Using the model of the Atlantic islands, the crown in 1536 divided the Brazilian coast into fifteen donatory captaincies (donatários ). To induce settlement, the crown offered ten leagues of coastline as personal property, a percentage of the dyewood trade, control over trade of enslaved natives, as well as the exclusive right to build mills. In 1580 Brazil comprised the area from Pernambuco in the north to São Vicente in the south. With Spanish assistance thereafter, the Portuguese expanded north to Paraíba, then west through Ceará and Maranhão against the natives and the French, until they founded Belém in 1616. Beginning in 1621, these possessions were divided into the state of Maranhão (embracing the crown captaincies of Ceará, Maranhão, and Pará) and the state of Brazil, centering on Salvador, Bahia. The reassertion of Portuguese independence under the Braganças in 1640 led to sporadic conflict in frontier areas and to policies seeking to hold back Spanish advances. In the Amazon and Río de la Plata river basins, the Spanish rather than the Portuguese had been first on the scene. The Spaniards included Álvar Núñez Cabeza de Vaca, who journeyed from the coast of Santa Catarina to Asunción in 1540, and Francisco de Orellana, who descended the Amazon in 1542.

The most important Spanish advances were the mission settlements, where the Jesuits Christianized native peoples. Two areas of particular importance lay adjacent to the river systems that delimit Brazil in the south and in the north: the Paraná-Paraguay Basin in the south and the Mamoré-Guaporé Basin in the north. From 1609 to 1628, the Jesuits founded eight missions among the Guaraní peoples between the Paraná and Paraguai rivers in what is now southern Paraguay. They pressed deep into what is today the state of Paraná, between the Ivaí and Paranapanema rivers, to establish fifteen more in what was called Guairá Province.

From 1629 to 1631, the Guairá missions were attacked by slave hunters, known as bandeirantes (see Glossary), from the Portuguese town of São Paulo. According to the governor of Buenos Aires, these attacks resulted in the enslavement of more than 70,000 Guaraní. Consequently, the Jesuits decided to evacuate some 10,000 survivors downriver and overland to sites between the Rio Uruguai and the Atlantic, in what became the state of Rio Grande do Sul. Other Jesuits fleeing the Guairá missions set up missions among the Itatín people on the eastern bank of the Rio Paraguai in what is now Mato Grosso do Sul, only to be destroyed brutally by bandeirantes in the 1630s and 1640s. By 1650 only twenty-two of forty-eight missions remained in the whole region. The Jesuits stopped the slave hunters in the south by arming and training the Guaraní, who dealt a significant blow to their oppressors in the Battle of Mbororé in 1641. This victory ensured the continued existence of the southern Spanish missions for another century, although they became a focal point of Portuguese-Spanish conflict in the 1750s. Broadly speaking, the Battle of Mbororé stabilized the general boundary lines between the Portuguese and the Spanish in the south.

In the north, the Spanish had established the town of Santa Cruz de la Sierra in 1561 and from there planted missions in the Mamoré-Guaporé Basin in about 1682. Called the Mojos and Chiquitos, these mission provinces were in what is now lowland Bolivia fronting on the states of Mato Grosso and Rondônia. By 1746 there were twenty-four mission towns in the Mojos and ten in Chiquitos. The bandeirantes again carried the flag of Portugal into the region, first attacking the Chiquitos missions for slaves and then discovering gold in Mato Grosso (1718-36). Unsure where these gold discoveries were in relation to the Spanish territories, the members of the Lisbon-based Overseas Council, which administered the colonies, ordered a comprehensive reconnaissance and the drawing of accurate maps. In 1723 Francisco de Melo Palhêta led an expedition from Belém to the Guaporé, reporting to Lisbon the startling news about the numerous prosperous Jesuit missions. Moreover, the question of fixing borders had become more urgent in 1722, when a respected French cartographer placed the mouths of the Amazon and the Río de la Plata on the Spanish side of the Tordesillas Line.

Because the Guaporé rises in Mato Grosso and flows into the Mamoré, which enters the Madeira, and then into the Amazon, these rivers formed a natural border. Moreover, the headwaters of the Paraguai were close and offered the possibility of linking the Amazonian and La Plata systems. In 1748 Lisbon created the Captaincy of Mato Grosso as its rampart on the Peruvian side and later in the century erected Fort Príncipe de Beira on the Guaporé. In northern Amazônia, in what were then the royal states of Maranhão and Pará, the Portuguese, worried about Dutch traders from Guiana (modern Suriname) and Spaniards from Venezuela, built fortifications at Óbidos, Manaus, Tabatinga, and on the Rio Branco and Rio Negro during the eighteenth century, thereby solidifying their claims. As it turned out, it was easier to secure the vast North region than it was the South.

In 1680 the Portuguese had built a fort at Colônia do Sacramento on the eastern La Plata shore opposite Buenos Aires to guard their claim and to capture a share of the contraband trade with silver-rich Potosí. According to the Overseas Council, Lisbon adopted the policy of fortifying and settling the coast below Santa Catarina, because "the continuation of these settlements will be the best means of deciding the question of limits . . . between the two crowns."

By the mid-eighteenth century, the Iberian powers were ready to admit the fiction of Tordesillas and to redraw their lines in South America on the basis of uti possidetis (that is, ownership by occupation rather than by claim). The Portuguese gave up Colônia do Sacramento, and in return received the lands of the Jesuit order's seven missions in western Rio Grande. This exchange led to the Guaraní War of 1756, which destroyed the missions and contributed to the Jesuit expulsion from Portuguese (1759) and Spanish (1763) possessions. With the Treaties of 1750, 1761, and 1777, Brazil took on its modern shape. The lines were drawn for the nineteenth-century struggles over the East Bank (Banda Oriental, or present-day Uruguay) of the Rio Uruguai and the Río de la Plata, the war with the United Provinces of the Río de la Plata (1825-28), and the Paraguayan War, also known as the War of the Triple Alliance (1864-70).

Thus, as a result of slave hunting, gold prospecting, and Portuguese royal policy, the Tordesillas Line became obsolete, and Portugal obtained more than half of South America. When Brazil became independent in 1822, its huge territory was comparable in size with the Russian and Chinese empires.

Data as of April 1997