Portugal established the first and longest-lasting of Europe’s overseas empires, developing a maritime-commercial network that connected the Atlantic, Indian, and Pacific Oceans from the 15th century onward. Under rulers such as João I (reign 1385 to 1433), Henry the Navigator (1394–1460), João II (reign 1481 to 1495), and Manuel I (reign 1495 to 1521), Portuguese expansion was driven by the pursuit of direct access to the spice markets of Asia, control of strategic maritime chokepoints, and competition with Islamic and Venetian trade networks. Rather than creating a continuous territorial empire, Portugal established a system of fortified ports, naval patrols, treaty alliances, and commercial monopolies stretching from West Africa and Brazil to India, Southeast Asia, China, and Japan.

The conquest of Ceuta in 1415 marked the symbolic beginning of Portuguese overseas expansion, extending the spirit of the Reconquista into North Africa. During the 15th century, Portuguese navigators gradually explored the Atlantic islands and West African coast, aided by advances in cartography, shipbuilding, and navigation. Bartolomeu Dias rounded the Cape of Good Hope in 1488, and Vasco da Gama reached India in 1498, opening a direct maritime route between Europe and the Indian Ocean trade world. By circa 1580, Portugal had established major commercial and strategic centers at Goa, Hormuz, Malacca, Macau, Mozambique, and along the Atlantic coast of Brazil. The year 1580 also marked a major turning point: after the death of Sebastian I of Portugal (reign 1557–1578) in Morocco and the resulting succession crisis, Philip II of Spain (reign 1556–1598) became Philip I of Portugal (reign 1581–1598), creating the Iberian Union (1580–1640).