Charles V inherited a vast empire that stretched from one end of Europe to the other. He acquired the Spanish throne from his parents, Philip I and Queen Joan , and his maternal grandparents and Burgundy through his father’s mother —who had been the duchess of Burgundy. His claim to the Habsburg throne came from his father’s father, Maximilian I . Maximilian had also been the Holy Roman emperor, a seat to which one was elected. Charles V won the electoral votes necessary to secure his own claim to the empire by, among other things, touting his descent from Maximilian.

Charles V abdicated the throne in 1556, apportioning his imperial titles to his brother Ferdinand I and his Dutch and Spanish ones to his son Philip II . His ill health, particularly his decades-long battle with gout , was undeniably a factor in his decision to abdicate. His writings also reveal the weariness that a reign’s worth of wars had instilled in him. It’s unclear what his contemporaries thought about his abdication, although the writings left behind by St. Ignatius of Loyola indicate that he, at least, regarded it favourably—as a humble move that befit a “true Christian prince.”

Charles V spent his reign trying to maintain the integrity of the Holy Roman Empire against the many forces that sought to undermine it. An emerging Protestantism proved to be one of the biggest internal threats. Although the papacy lent Charles V military and fiscal aid in the fight against the Protestants, it was occasionally a thorn in the emperor’s side, particularly when it was allied with Charles’s longtime nemesis, King Francis I of France. The biggest external menace to Europe came from the Ottoman Empire , which applied pressure from the east for much of Charles’s rule.

Although establishing a universal empire was chief among Charles V’s goals as Holy Roman emperor, he was unable to do so. Protestantism ’s growing momentum made it impossible for Charles to prevent the fragmentation of his Catholic empire, and his attempts to unite Europe were further confounded by his enmity with France. He was also unable to establish profitable landholdings overseas: his attempts to conquer North Africa failed, and Spain’s territories in the Americas wouldn’t become lucrative until the reigns of later kings. Charles V abdicated in 1556 without achieving his goal of a universal empire.

In September 1517 he arrived in Spain, a country with whose customs he was unfamiliar and whose language he was as yet barely able to speak. There he instituted, under Burgundian influence, a government that was little better than foreign rule. When his election as king of Germany in 1519 (succeeding his grandfather Emperor Maximilian I) recalled him to that country after some two and one-half years in Spain, Charles left behind him a dissatisfied and restless people. Adrian, whom he had installed as regent, was not strong enough to suppress the revolt of the Castilian cities ( comuneros ) that broke out at that point. Making the most of their candidate’s German parentage and buying up German electoral votes (mostly with money supplied by the powerful Fugger banking family), Charles’s adherents had meanwhile pushed through his election as emperor over his powerful rival, Francis I of France .

In 1515 Charles came of age as duke of Burgundy and assumed rule over the Netherlands. His scope of activities soon widened. On January 23, 1516, Ferdinand II died. As a result, the problem of the succession in Spain became acute , since by the terms of Ferdinand’s will, Charles was to govern in Aragon and Castile together with his mother (who, however, suffered from a nervous illness and never reigned). Furthermore, the will provided that Francisco, Cardinal Jiménez de Cisneros , who was the archbishop of Toledo and one of Ferdinand and Isabella’s most-influential advisers, should direct the administration in Castile. The Spanish opponents of Ferdinand who had fled to Brussels succeeded in having the will set aside, however, and on March 14, 1516, Charles was proclaimed king in Brussels as Charles I of Aragon and Castile.

Imperialist goals, rivalry with Francis I, and fight against Protestantism

In October 1520 Charles was accordingly crowned king of Germany in Aachen, assuming at the same time the title of Roman emperor-elect. In the spring of 1521 the imperial Diet, before which Martin Luther had to defend his theses, assembled at Worms. The reformer’s appearance represented a first challenge to Charles, beginning with a sweeping invocation of his Roman Catholic ancestors, read out to the Diet. After Luther refused to recant the substance of his writings and left the Diet, Charles drew up the Edict of Worms. With it, he rejected Luther’s doctrines and essentially declared war on Protestantism.

Gradually, the other chief task of his reign also unfolded: the struggle for hegemony in western Europe. That goal was a legacy of his Burgundian forefathers, including his ancestor Charles the Bold, who had come to naught in his fight against the French Valois Louis XI. His great-grandfather’s quest was to become a fateful problem for Charles as well.

Charles V; Titian Charles V, detail of an oil painting by Titian, 1548; in the Bayerische Staatsgemäldesammlungen, Munich, Germany. Courtesy of the Bayerische Staatsgemaldesammlungen, Munich

After defeating Duke Massimiliano Sforza at the Battle of Marignano in 1515, Francis I of France compelled him, in the Treaty of Noyon, to renounce his claim to the duchy of Milan. The vanquished Sforza turned for help to Pope Leo X and Charles V, with whom he concluded a treaty in 1521. Despite the outbreak of war with France, Charles hurried back to Spain, where his followers had meanwhile gained the upper hand over the comuneros. Even though he granted an amnesty, the young monarch proved to be an intransigent ruler, bloodily suppressing the revolt and signing 270 death warrants. Those actions were nevertheless followed by a rapid and complete rapprochement between the pacified people and their sovereign; in fact, it was during that second and protracted sojourn in Spain (1522–29) that Charles became a Spaniard, with Castilian grandees replacing the Burgundians. There soon developed an emotionally tinged understanding between Charles and his Spanish subjects that was to be steadily deepened during his long rule. Henceforth, it was primarily the material resources of his Spanish domains that sustained his far-flung policies and his Spanish troops who acquitted themselves most bravely and successfully in his wars.

In 1522 his teacher Adrian of Utrecht became pope, as Adrian VI. His efforts to reconcile Francis I and the emperor failed, and three years later Charles’s army defeated Francis I at the Battle of Pavia, taking prisoner the king himself. The victory ensured Spanish supremacy in Italy. Held in the alcazar of Madrid, the royal captive feigned agreement with the conditions imposed by Charles, even taking the emperor’s oldest sister, Eleanora, the dowager queen of Portugal, for his wife and handing over his sons as hostages. The Treaty of Madrid concluding hostilities between the two countries was signed in January 1526, but as soon as he had regained his freedom, Francis rejected the treaty and refused to ratify it.

With the accession of Süleyman the Magnificent to the Ottoman sultanate in 1520, Turkish pressure on Europe increased once more. The sultan threatened not only Hungary but also those hereditary provinces of the Habsburgs that, by Charles’s agreement in 1522 with his brother Ferdinand, thenceforth belonged to the younger branch of the Habsburgs. When Louis II of Hungary and Bohemia was defeated and killed by the Ottoman Turks in the Battle of Mohács in August 1526, Ferdinand assumed his throne both as the childless former monarch’s brother-in-law and by virtue of the treaty of succession concluded in 1491 between his own grandfather and Louis’s father, Vladislas II. After that, the Turkish danger became the Habsburgs’ foremost concern on land, as it had been on the seas ever since Charles’s accession to the throne of Spain. Although Charles realized that his first duty as emperor of Christendom lay in warding off that peril, he found himself so enmeshed in the affairs of western Europe that he had little time, energy, and money left for the task. In 1526 Charles married Isabella, the daughter of the late king Manuel I of Portugal.

In early 1527, instead of fighting the Turks, Charles’s Spanish troops and his German mercenaries marched against Pope Clement VII, who had been his enemy since the establishment of the League of Cognac, the pope’s alliance with France, Venice, Florence, and Milan against the emperor. Mutinous and with their pay in arrears, Charles’s forces entered the defenseless city of Rome and looted it during the infamous sack of Rome (May 1527).

The pope, having surrendered to the mutinous troops, was ready for any compromise. The newly started war between the emperor and France also came to a close when the mother of Francis I approached Margaret of Austria, the emperor’s aunt, through whose mediation the so-called “ladies’ peace,” the Treaty of Cambrai, was concluded in August 1529. The status quo was preserved: Charles renounced his claim to Burgundy; Francis, his claims to Milan and Naples. The pope, having made peace with Charles, met him in Bologna; there he crowned him emperor in February 1530. It was to be the last time that a Holy Roman emperor was crowned by a pope.

In 1530 Charles, attempting to bring about a reformation within the Roman Catholic Church through the convocation of a universal council, also tried to find a modus vivendi with the Protestants. The Roman Catholics, however, condemned the Augsburg Confession—the basic confession of the Lutheran doctrine faith presented to Charles at the Diet of Augsburg—and responded with the Confutation, which met with Charles’s approval. The final decree issued by the Diet accordingly confirmed, in somewhat expanded form, the resolutions embodied in the Edict of Worms of 1521. That, in turn, caused the Protestant princes to close ranks in the following year in the Schmalkaldic League. Faced with renewed Turkish onslaughts, the emperor granted some concessions in return for armed support against the enemy. In 1532 a large army under Charles’s personal command faced Süleyman’s forces before the city of Vienna, but the order to give decisive battle was withheld. Instead, the emperor returned to Spain in 1533, leaving his brother Ferdinand behind as his deputy.

By taking up his grandfather Ferdinand of Aragon’s project of conquering North Africa, Charles endeavoured to undertake by sea what he had not done on land. The attempt to repulse the corsair (and admiral of the Ottoman fleet) Barbarossa (Khayr al-Dīn) was nonetheless no more than a marginal operation, since Charles’s capture of La Goulette (Ḥalq al-Wādī) and Tunis (1535) did nothing to diminish the strength of Süleyman’s position.

From Africa the emperor sailed to Naples, entering Rome in 1536 to deliver his famous political address before Pope Paul III and the Sacred College of Cardinals in which he challenged the king of France (who had meanwhile invaded Savoy and taken Turin) to personal combat. When Francis declined, Charles invaded Provence in an operation that soon faltered. Through the pope’s intercession, a peace agreement, the Truce of Nice, was concluded in June 1538.

Intent on suppressing the open revolt that had broken out in Ghent, his native city, the emperor himself went to the Netherlands. The country’s regent—Charles’s sister, Mary of Hungary—had proved incapable of settling the conflict between herself and the city, which jealously guarded its prerogatives. On his arrival in February 1540, Charles revoked Ghent’s privileges, had 13 leading rebels executed, and gave orders to build a fortified castle. Once again his actions, as severe as those he had taken against the comuneros in 1522, were crowned by success. Toward the German Protestants, on the other hand, he showed himself conciliatory; in 1541 the Diet of Regensburg granted them major concessions, even if those were later rejected by both the pope and Luther. Although Ferdinand, having lost his Hungarian capital in August 1541, pleaded for a land campaign against Süleyman I, Charles again decided on a naval venture, which failed dismally after an unsuccessful attack on Algiers.

When Charles granted his son Philip the duchy of Milan, the king of France, enraged because he had hoped to regain indirect control of Milan himself, rearmed and declared war in August 1542. Fighting broke out the following year, even though the pope had finally convoked, in Trent (Trento, Italy), the council for which the emperor had been pressing. Once again Charles’s precarious financial situation partially accounted for the failure of his plans. His finances were in a perpetually unsettled state. The Spanish possessions in the New World were, of course, in an uninterrupted state of expansion throughout his entire reign, marked by, among other ventures, the conquest of Mexico and the conquest of Peru. The gold from those possessions did not add up to any sizable sum at the time. Only in 1550 did 17 Spanish ships provide the emperor with 3,000,000 ducats and others with a like sum, the earliest significant monetary transfusion from the New World. The silver mines of Potosí were not exploited systematically until the 1550s; thus, their revenue arrived too late for Charles. In 1516 Spain’s floating debt amounted to 20,000 livres; by 1556 it had risen to 7,000,000. In 1556 the exchequer owed 6,761,272 ducats. Thus, the campaign of 1543–44, inadequately financed, bogged down. It was to no avail that the French and imperial armies faced one another in the field in November 1543 and again in August 1544. As in 1532, when Charles had faced the Ottoman Turks before Vienna, neither side cared to open hostilities, with the result that the Peace of Crépy (September 1544) again more or less confirmed the status quo.

The Council of Trent did not open until December 1545, but Paul III had earlier offered Charles men and money against the heretics. When the Protestant princes failed to put in an appearance at the imperial Diet of Regensburg in 1546, the religious and political situation turned critical once again. Charles prepared for war. In a battle that decided the whole campaign and placed his archenemies at his mercy, the emperor (who had been attacked by the German princes the previous September) defeated the Protestants at Mühlberg in April 1547. Ill much of the time, he spent the following year at Augsburg, where he succeeded in detaching the Netherlands from the imperial Diet’s jurisdiction while yet assuring their continued protection by the empire. Also while in Augsburg, Charles drew up his “political testament” for Philip and reorganized the Spanish court. The Diet of Augsburg furthermore saw the publication of the “Interim,” a formula conciliatory to the Protestants but retaining the Roman Catholic ritual in general. Although Charles believed that he had granted far-reaching concessions to the people and the Protestant authorities in that document, his main concern was to make the Protestants return to the Roman Catholic Church.

North Germany was now on the brink of revolt. The new king of France, Henry II, was eagerly awaiting an opportunity to renew the old rivalry between the houses of Valois and Burgundy, while the German princes believed that the moment was at hand to repay Charles for Mühlberg. After a secret treaty was signed in October 1551 between Henry II, Albert II Alcibiades, margrave of Brandenburg, and Maurice, elector of Saxony, Maurice in January 1552 ceded to France the cities of Metz, Toul, and Verdun, thus handing over imperial lands. When Maurice tried to capture the emperor himself, the latter barely managed to escape. He soon gathered reinforcements, but the changed political situation compelled him to ratify an agreement made between his brother Ferdinand and the rebels, according to which the new Protestant religion was to be granted equal rights with Roman Catholicism. Charles’s attempt to retake Metz that fall ended in a complete fiasco, with Burgundy capitulating to Valois and the emperor defeated in his struggle for hegemony in western Europe.

In order to save what he could of that hegemony, Charles, already severely racked by gout, tried new paths by preparing the ground for his widowed son’s marriage with Mary I of England. It looked for a while as if his great hopes were about to be fulfilled, the joining of north and south and the realization of the dream of a universal empire. But, even though Philip married Mary in July 1554, the English Parliament emphatically refused to crown him. Since Mary remained childless, Charles’s hopes came to naught. After an abortive last campaign against France, he prepared for his abdication, renouncing, in 1555 and 1556, his claims to the Netherlands and Spain in favour of Philip and those to the imperial crown in Ferdinand’s favour. He disembarked in Spain at the end of September 1556 and moved to the monastery of Yuste, which he had long before selected as his final refuge, in early February 1557. There he laid the groundwork for the eventual bequest of Portugal to the Habsburgs after the eventual death of King Sebastian (who was then still a child) with the help of his sister Catherine, grandmother of Sebastian and regent of Portugal. He aided his son in procuring funds in Spain for the continuation of the war against France, and he helped his daughter Joan, regent of Spain during Philip’s absence in the Netherlands, in persecuting Spanish heretics.