1494: How a Family Feud in Medieval Spain Divided the World in Half

In 1493, Columbus's return to Spain reignited a conflict between Spain's monarchs Ferdinand and Isabella and Portugal's João II over control of the world's oceans. Pope Alexander VI issued a proclamation that led to the Treaty of Tordesillas in 1494, which drew an imaginary line across the Atlantic Ocean dividing the known and unknown world between Spain and Portugal. The treaty elevated both nations to superpower status but also set other European powers on a collision course, becoming the central cause of two centuries of international espionage, piracy, and warfare. It sparked the struggle for "the freedom of the seas"—a debate over whether oceans and global commerce would be controlled by decree or open to all nations. Dutch legal theorist Hugo Grotius championed this idea in the early seventeenth century, laying the foundation for international law. The treaty's origins lay in the personal relationships, rivalries, and hatreds of powerful individuals including Ferdinand and Isabella, Columbus, Magellan, Sir Francis Drake, and the Borgia family. Ultimately, the conflict stemmed from a young woman's determination to defy tradition and choose her own husband.