Shortly before his death in November 1700, Charles named Philip his heir, but the acquisition of an undivided Spanish Empire by either France or Austria threatened the European balance of power.

[4] A 2019 study based on an analysis of Habsburg portraits concluded this feature was likely due to a recessive trait, but in the absence of genetic material such claims remain speculative.

[6] Based on an analysis of contemporary accounts, some modern researchers argue they may have been due to one or more autosomal recessive disorders,[7][8] others suggest an herpetic infection incurred as an infant, causing hydrocephalus.

[14] From the age of 12, he received lessons in music from Juan del Vado, and in mathematics by Jose Zaragoza, Professor at the Colegio Imperial de Madrid.

[16] One often cited example of his alleged mental incapacity is the period he spent sleeping with his father's disinterred body; this was in fact done under instructions from Mariana, whose doctors advised this would help him produce an heir.

[17] Although reputedly subject to bouts of depression, his participation in government and reports from his council and foreign observers such as the French ambassador Jean-Baptiste Colbert, Marquess of Torcy, indicate his mental capacities remained intact.

The Spanish Empire remained an enormous global confederation, but its economic supremacy was increasingly challenged by the Dutch Republic and England, and its position in Europe destabilised by the expansionist policies of Louis XIV of France.

Her ability to respond effectively to the challenges facing the Empire was hampered by an ongoing power struggle with John Joseph of Austria, hereafter referred to as Don Juan, Charles's older, illegitimate half-brother.

In 1663, Philip IV had converted state debt into government bonds, or juros, but high rates of interest meant taxes were often assigned to creditors years in advance to pay current liabilities.

The Marqués de Varinas, a senior colonial official, observed in 1687 that the Empire continued to exist in its present form "only because it enables the English, Dutch and French to exploit [it] more cheaply".

[g][39] A new wife was selected from a family famous for its fertility, Maria Anna of Neuburg, daughter of Philip William, Elector Palatine, and sister-in-law to Emperor Leopold.

However, to prevent a union between Spain and France, Maria Theresa had renounced her inheritance rights on her marriage; in return, Louis was promised a dowry of 500,000 gold écus, a huge sum that was never paid.

[42] The Nine Years' War showed France could not achieve its objectives on its own; the 1697 Treaty of Ryswick was the result of mutual exhaustion and Louis's search for allies in anticipation of a contest over the Spanish throne.

[43] In 1685, Leopold and Margaret's daughter Maria Antonia married Maximilian II Emanuel, Elector of Bavaria; she died in 1692, leaving one surviving son, Joseph Ferdinand.

This made Joseph Ferdinand heir to the bulk of the Spanish monarchy, with France gaining the Kingdoms of Naples and Sicily and other concessions in Italy plus the modern Basque province of Gipuzkoa.

Leopold's younger son Archduke Charles became ruler of the Duchy of Milan, a possession considered vital to the security of Austria's southern border.

The autopsy records his "heart was the size of a peppercorn; his lungs corroded; his intestines rotten and gangrenous; he had a single testicle, black as coal, and his head was full of water.

[50] Despite their disastrous short-term impact, the financial measures taken by his advisors ended the chronic instability which had affected the Spanish currency throughout the 17th century, and helped drive sustainable economic growth.

When Charles changed his will in favour of Philip in 1700, the Inquisitor General Baltasar de Mendoza y Sandoval, an ally of Maria Anna, arrested his personal confessor Froilán Díaz on a charge of 'bewitching' the King.

When Díaz was found not guilty, Mendoza attempted to arrest those who voted for his acquittal, resulting in the establishment of a Council to investigate the Inquisition; although it survived until 1834, its influence had ended.

[56] Formalised in 1733 by Philip, it led to the founding in 1738 of Santa Teresa de Mose, the first legally sanctioned free black town in the present-day United States.