Although the relationship does not appear to have been close, some have suggested that Gaspar de Guzmán, Count-Duke of Olivares, his key minister, later deliberately tried to keep the two apart to maintain his influence, encouraging Philip to take mistresses instead, by whom he is known to have had at least 30 progeny.

Maria Anna bore him five children, but only two survived to adulthood, a daughter Margarita Teresa, born in 1651, and the future Charles II of Spain in 1661 – but the latter was sickly and considered in frequent danger of dying, making the line of inheritance potentially uncertain.

[4] By the end of the reign, and with the health of Carlos, Prince of Asturias in doubt, there was a real possibility of Juan José's claiming the throne, which added to the instability of the regency years.

In Philip III's final years, Baltasar de Zúñiga had convinced him to intervene militarily in Bohemia and the Electoral Palatinate on the side of Ferdinand II, Holy Roman Emperor.

This lead Philip to renew hostilities with the Dutch in 1621 in an attempt to bring the provinces to the negotiating table with the aim of achieving a peace treaty favourable to Spanish global interests.

Philip's advisors recommended prioritising the war in Flanders, taking action to safeguard the Spanish Road to the Netherlands but at the cost of antagonising Louis XIII.

But from 1640 onwards, a period which saw large-scale revolts across Spanish territories in protest against the rising costs of the conflict, Spain was finding it difficult to sustain the war.

Philip reacted to the increased French threat by finally abandoning his 'Netherlands first' strategy; resources for the Army of Flanders were savagely cut, and the fight against the French-supported rebels in Catalonia took the first priority.

Philip responded to the perceived weakness of France during the Fronde rebellions of 1648 by continuing the fight; he took personal responsibility for the decision to start a fresh, and ultimately successful, offensive against the French in Catalonia in 1651.

[39] The Treaty of the Pyrenees in 1659, and the marriage of Philip's daughter Maria Theresa to the young King Louis XIV[40] finally brought the war with France to a conclusion.

[citation needed] In keeping with their wider agenda of renewing the concepts of duty, service and aristocratic tradition, the King agreed to efforts to introduce more grandees into the higher ranks of the military, working hard to overcome the reluctance of many to take up field appointments in the Netherlands and elsewhere.

The grandees dragooned into service in this way were disinclined to spend years learning the normal professional military skill set; they wished 'to start out as generals and soldiers on the same day', to quote one disgruntled career soldier.[who?]

By the 1630s, the King was waiving the usual rules to enable promotion to higher ranks on a shorter timescale, and having to pay significantly inflated salaries to get grandees to take up even these appointments.

In 1640, Philip IV's initial strategy to undermine the new Portuguese government involved dividing the extensive border shared between Portugal and Castile into military districts.

Some of his conclusions on naval policy were quite advanced: after the peace of 1648, Philip argued that the Dutch fleets off the Spanish peninsula were actually good for trade, despite concerns from his senior officials, since they provided protection against the English and French navies.

This loose system had successfully resisted reform and higher taxation before, ironically resulting in Spain's having had historically, up until the 1640s at least, fewer than the usual number of fiscal revolts for an early modern European state.

In 1623, he closed all the legal brothels in Spain, extended the dormant sumptuary laws on luxury goods and supported Papal efforts to regulate priests' sexual behaviour more tightly.

[59] Financial restraints and higher taxes were put in place, but Philip was increasingly selling off regalian and feudal rights, along with much of the royal estate to fund the conflict.

[60] It has been argued that the fiscal stringencies of the 1630s, combined with the strength and role of Olivares and the juntas, effectively cut Philip off from the three traditional pillars of support for the monarchy: the grandees, the Church and the Council of Castile.

An alliance of Catalan rebels and French royal forces proved challenging to suppress, and in trying to mobilise Portuguese noble support for the war, Olivares triggered a second uprising.

Lisbon's nobles expelled Philip, and gave the throne to the House of Braganza, marking the end of sixty years of the Iberian Union and the beginning of the Portuguese Restoration War.

[70] Philip was nicknamed el Rey Planeta, the 'Planet King',[71] by his contemporaries, and much of the art and display at his court has been interpreted in the context of his need to project power and authority, over both Spaniards and foreigners alike.

[72] Older interpretations, which perceived Philip's court as being completely decadent, have been largely superseded, but the art and symbolism of the period certainly did not reflect the wider threat and decline of Spanish power.

Numerous artists from the Spanish Netherlands produced work extolling the Army of Flanders, including Sebastian Vrancx, Peter Snayers, Jan Miense Molenaer and Willem Hondius.

Given both its cost, in a time of stringent wartime savings, and the protest that ensued from a disgruntled public,[73] it is considered to have been an important part of the attempt to communicate royal grandeur and authority.

[74] As well as marking a strong personal religious belief, this increasingly visible link between the crown, the Church and national symbols such as the Virgin of Miracles, represented a key pillar of support for Philip as king.

Philip, for example, keen to reach out to his Portuguese subjects, put his considerable influence behind the case for Isabella of Portugal, a 14th-century role model of a 'perfect queen', to great effect, ultimately paying for a lavish celebration in Lisbon after her canonisation in 1625.

Queen Isabella and the new president of the Council of Castile, Don Juan Chumacero – both involved in the removal of Olivares – encouraged the King to invite mystics and visionaries from across Europe to his court at Zaragoza.

[78] In the Treaty of Münster (1648), he was styled "Don Philip the Fourth, by the grace of God king of Castile, Leon, Aragon, the Two Sicilies, Jerusalem, Navarre, Granada, Toledo, Valencia, Galicia, Majorca, Minorca, Seville, Sardinia, Cordoba, Corsica, Murcia, Jaen, Algeciras, Gibraltar, the Canary Islands, the Eastern and Western Indies, the islands and terra firma of the Ocean, archduke of Austria, duke of Burgundy, Brabant, Milan, count of Habsburg, Flanders, Tyrol, Barcelona, lord of Biscay and Molina, etc."

In his will, Philip left political power as regent on behalf of the young Charles II to his wife Mariana, with instructions that she heed the advice of a small junta committee established for this purpose.