Philip IV of Spain

For much of his long reign, Philip IV (1605-1665) presided over Spain's costly effort to maintain primacy in Europe, and over its visible decline. The son of Philip III and Margaret of Austria, he came to the throne in 1621 at sixteen and gave his confidence to Gaspar de Guzmán, Count-Duke of Olivares, who directed policy for the next two decades. Olivares pursued reputación abroad and reform at home, including the unrealized Union of Arms, a scheme to spread military burdens among the monarchy's kingdoms beyond overtaxed Castile.

War framed the reign. The Twelve Years' Truce with the Dutch lapsed in 1621 and the war resumed; Spain fought alongside the Austrian Habsburgs in the Thirty Years' War, winning notable successes in the 1620s and at Nördlingen in 1634, where Spanish and imperial cousins commanded together. Open war with Bourbon France from 1635 stretched resources past breaking. In 1640 both Catalonia and Portugal revolted; Catalonia was recovered by 1652, but Portugal, under the Braganza dynasty, was never regained in Philip's lifetime. Olivares fell in 1643, the year of the defeat at Rocroi. At the Peace of Westphalia in 1648 Spain finally recognized Dutch independence, and the Peace of the Pyrenees in 1659 ended the French war with territorial concessions and the marriage of Philip's daughter Maria Theresa to Louis XIV — a union whose renounced but unpaid dowry later furnished French claims on the Spanish inheritance.

Philip's first wife, Elisabeth of France, died in 1644; their son Baltasar Carlos, the heir, died in 1646. To secure the succession Philip then married his niece Mariana of Austria, daughter of Emperor Ferdinand III, who had been intended for Baltasar Carlos — an extreme instance of the intermarriage habitual between the two Habsburg branches. Their daughter Margarita Teresa married Emperor Leopold I; of their sons, only the frail Charles survived.

A discerning patron, Philip employed Diego Velázquez as court painter, assembled one of Europe's great picture collections, and built the Buen Retiro palace; the era of Calderón and Zurbarán coincided with the monarchy's political ebb. He died in Madrid on 17 September 1665, leaving the throne to the three-year-old Charles II under Mariana's regency.