A In the 15th and 16th centuries Portugal, with barely a million inhabitants, was hemmed in by the Atlantic to the west and a hostile Castile to the east. After years of struggle against the Moorish occupation, the Portuguese looked to the sea and what lay beyond. While the Spaniards set out in search of a route to the Orient by voyaging to the West, the Portuguese opted for the so-called Southern Cycle down the African coast. Reaching the Cape of Good Hope in 1487, they proved a sea route to the Far East across the Indian Ocean in 1497. They knew of the existence of lands across the Atlantic and they had made several expeditions to the West before Columbus discovered the Antilles in 1492. But they had kept the knowledge to themselves in order to thwart the ambitions of Spain, England, and France.Secrecy was the only available method of safeguarding the rewards of successful exploration against exploitation by more powerful maritime rivals.

The Treaty of Tordesillas (1494) settled possession of the new lands between Spain and Portugal. It was agreed that territories lying east of a meridian 370 leagues west of the Cape Verde Islands should belong to Portugal, the lands to the west to Spain. This imaginary line, from pole to pole, cut through the easternmost part of the South American continent and constituted Brazil's first frontier, although the formal discovery by Pedro Álvares Cabral did not take place until six years later in 1500.