By the time Christopher Columbus started setting east from the New World, he had explored San Salvador in the Bahamas (which he thought was Japan), Cuba (which he thought was China), and Hispaniola, the source of gold. As the common story goes, Columbus, en route back to Spain from his first journey, called in at Lisbon as a courtesy to brief the Portuguese King John II of his discovery of the New World. King John subsequently protested that according to the 1479 Treaty of Alcáçovas, which divided the Atlantic Ocean between Spanish and Portuguese spheres of influence, the newly discovered lands rightly belonged to Portugal. To make clear the point, a Portuguese fleet was authorized and dispatched west from the Tagus to lay claim to the “Indies,” which prompted a flurry of diplomatic activity in the court of Ferdinand and Isabella. At the time, Spain lacked the naval power to prevent Portugal from acting on this threat, and the result was the hugely influential 1494 Treaty of Tordesillas.

The Treaty of Tordesillas was one of the most important documents of its kind of the age, for it established the essential parameters of the two competing empires, the first of the major European imperial entities. The Treaty of Tordesillas drew an imaginary line from pole to pole, running 100 leagues west of the westernmost islands of the Azores. According to the terms of a supporting papal bull, all the lands to the west of that belonged to Spain, and all of those to the east belonged to Portugal. What this meant in practical terms was that Portugal was given Africa and the Indian Ocean while Spain was granted all the lands to the west, including the Americas and the Caribbean, all collectively known as the “Indies,” or the New World. Perhaps inevitably, a regional rivalry had developed as the Portuguese began to establish a colony in Brazil and push its boundaries southwards.