As the Reconquista continued, Christian kingdoms and principalities developed. By the 15th century, the most important among these were the Kingdom of Castile (occupying a northern and central portion of the Iberian Peninsula) and the Kingdom of Aragon (occupying northeastern portions of the peninsula). The rulers of these two kingdoms were allied with dynastic families in Portugal, France, and other neighboring kingdoms. The death of Henry IV in 1474 set off a struggle for power between contenders for the throne of Castile, including Joanna La Beltraneja, supported by Portugal and France, and Queen Isabella I, supported by the Kingdom of Aragon, and by the Castilian nobility. Following the War of the Castilian Succession, Isabella retained the throne, and ruled jointly with her husband, King Ferdinand II. Isabella held more authority over the newly unified Spain than her husband, although their rule was shared.
Isabella of Castile and Ferdinand of Aragon were known as the "Catholic Monarchs" (Spanish: los Reyes Católicos), a title bestowed on them by Pope Alexander VI. They married in 1469 in Valladolid, uniting both crowns and setting the stage for the creation of the Kingdom of Spain, at the dawn of the modern era. That union, however, was a union in title only, as each region retained its own political and judicial structure, and even today Spain remains internally divided. The monarchs also oversaw the final stages of the Reconquista of Iberian territory from the Moors with the conquest of Granada, conquered the Canary Islands and expelled the Jews and Muslims from Spain under the Alhambra decree, though Muslim (Morisco) culture remained influential. They authorized the expedition of Christopher Columbus, who became the first known European to reach the New World since Leif Ericson, which led to an influx of wealth into Spain, supplementing income from within Castile for the state that would prove to be a dominant power of Europe for the next two centuries.
Isabella ensured long-term political stability in Spain by arranging strategic marriages for each of her five children. Her firstborn, a daughter named Isabella, married Alfonso of Portugal, forging important ties between these two neighboring countries and hopefully to ensure future alliance, but Isabella soon died before giving birth to an heir. Juana, Isabella's second daughter, married into the Habsburg dynasty when she wed Philip the Handsome, the son of Maximilian I, King of Bohemia (Austria) and entitled to the crown of the Holy Roman Emperor. This ensured alliance with the Habsburgs and the Holy Roman Empire, a powerful, far-reaching territory that assured Spain's future political security. Isabella's first and only son, Juan, married Margaret of Austria, further maintaining ties with the Habsburg dynasty. Her fourth child, Maria, married Manuel I of Portugal, strengthening the link forged by her older sister's marriage. Her fifth child, Catherine, married Henry VIII, King of England and was mother to Queen Mary I.
Although until the 13th century religious minorities (Jews and Muslims) had enjoyed considerable tolerance in Castilla and Aragon - the only Christian kingdoms where Jews were not restricted from any professional occupation - the situation of the Jews collapsed over the 14th century, reaching a climax in 1391 with large scale massacres in every major city, with the exception of Ávila. Over the next century, half of the estimated 200,000 Spanish Jews converted to Christianity (becoming "conversos"). The final step was taken by the Catholic Monarchs, who, in 1492, ordered the remaining Jews to convert or face expulsion from Spain. Depending on different sources, the number of Jews actually expelled is estimated to be anywhere from 40,000 to 120,000 people. Over the following decades, Muslims faced the same fate and about 60 years after the Jews, they were also compelled to convert ("moriscos") or be expelled. Jews and Muslims were not the only people to be persecuted during this time period. Gypsies also endured a tragic fate: all Gypsy males were forced to serve in galleys between the age of 18 and 26 - which was equivalent to a death sentence - but the majority managed to hide and avoid arrest.