John II of Portugal

John II executed the Duke of Braganza for conspiracy and later personally stabbed the Duke of Viseu to death. These actions crushed the power of the high nobility, centralizing royal authority and eliminating internal opposition to his policies.

John II's committee of experts rejected Christopher Columbus's proposal for a westward voyage to Asia, judging the distance estimates to be inaccurate. This decision led Columbus to seek sponsorship from Spain, resulting in the Spanish discovery of the Americas.

John II sponsored Bartolomeu Dias's expedition that rounded the southern tip of Africa, naming it the Cape of Good Hope. This proved that a sea route to the Indian Ocean was possible, opening the way for future voyages to India.

John II negotiated the Treaty of Tordesillas with Spain, dividing the non-European world along a meridian 370 leagues west of the Cape Verde islands. This agreement secured Portuguese control over the route to India and later Brazil, shaping colonial boundaries for centuries.

John II commissioned the construction of a fleet and the preparation of a voyage to India under Vasco da Gama, though he died before the expedition departed. His planning and support for exploration laid the foundation for Portugal's maritime empire in Asia.