Forces of the Catholic Monarchs engage the combined Portuguese-Castilian armies of Afonso V and Prince John at the Battle of Toro.

The Catholic Monarchs were Queen Isabella I of Castile and King Ferdinand II of Aragon, whose marriage and joint rule marked the de facto unification of Spain. They were both from the House of Trastámara and were second cousins, as they were both descended from John I of Castile. To remove the obstacle that this consanguinity would otherwise have posed to their marriage under canon law, they were given a papal dispensation by Sixtus IV. They married on October 19, 1469, in the city of Valladolid; Isabella was 18 years old and Ferdinand a year younger. Most scholars generally accept that the unification of Spain can essentially be traced back to the marriage of Ferdinand and Isabella. Their reign was called by W.H. Prescott "the most glorious epoch in the annals of Spain."

Afonso V, also known as the African, was King of Portugal from 1438 until he died in 1481, with a brief interruption in 1477. The son of Edward, King of Portugal, and Eleanor of Aragon, Afonso acceded to the throne when he was only six years old. His early reign was marked by a struggle over the regency between his mother, Eleanor, and his uncle, Pedro, Duke of Coimbra. Pedro was appointed sole regent in 1439, but the Braganza faction at court continued to challenge his authority. Influenced by his other uncle, Afonso I, Duke of Braganza, the King dismissed Pedro in 1448 and defeated him in the Battle of Alfarrobeira in 1449.

John II, called the Perfect Prince, was King of Portugal from 1481 until his death in 1495, and also for a brief time in 1477. He is known for reestablishing the power of the Portuguese monarchy, reinvigorating the economy of Portugal, and renewing the Portuguese exploration of Africa and Asia.

The Battle of Toro was part of the War of the Castilian Succession, fought on 1 March 1476, near the city of Toro, between the Castilian-Aragonese troops of the Catholic Monarchs and the Portuguese-Castilian forces of Afonso V and Prince John of Portugal.