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

An exciting account of the feud between monarchs, clergy, and explorers that split the globe between Spain and Portugal and made the oceans a battleground ( Kirkus Reviews ).
When Columbus triumphantly returned to Spain in 1493, his discoveries inflamed an already-smoldering conflict between Spain's monarchs, Ferdinand and Isabella, and Portugal's João II. Which nation was to control the world's oceans? To quell the argument, Pope Alexander VI—the notorious Rodrigo Borgia—issued a proclamation laying the foundation for the Treaty of Tordesillas of 1494, an edict that created an imaginary line in the Atlantic Ocean dividing the entire known (and unknown) world between Spain and Portugal.
Just as the world's oceans were about to be opened by Columbus's epochal voyage, the treaty sought to limit the seas to these two favored Catholic nations. The edict had a profound influence on world history: it propelled Spain and Portugal to superpower status, steered other European nations on a collision course, and became the central grievance in two centuries of international espionage, piracy, and warfare.
It also began the fight for the freedom of the seas—the epic struggle to determine whether the oceans, and thus global commerce, would be controlled by an autocrat's decree or open to the ships of any nation—a distinctly modern notion championed in the early seventeenth century by Dutch legal theorist Hugo Grotius, whose arguments became the foundation of international law.
At the heart of one of the greatest international diplomatic and political agreements of the last five centuries were the strained relationships and passions of a handful of powerful individuals. They were linked by a shared history, mutual animosity, and personal obligations—quarrels, rivalries, and hatreds that dated back decades. Yet the struggle ultimately stemmed from a young woman's determination to defy tradition and the king, and to choose her own husband.
Incorporates a sprawling cast of characters, including Ferdinand and Isabella, Columbus, Magellan, Sir Francis Drake, and members of the ostentatious Borgia clan, into what is both a judicious synthesis of the surrounding scholarship and an entertaining look at the evolution of international law on the high seas. — Booklist
A starry love story, a tale of seething jealousies and subterfuge, a political imbroglio, and religious cruelties. It sounds like Shakespeare and it could have very well been the plot of one of his plays. — Toronto Star
An entertaining and elegantly written voyage into the treacherous seas of religious fanatics, greedy slavers, depraved autocrats, doomed indigenous peoples and desperately brave adventurers in search of fortune. — Globe & Mail