While the Cleves-Jülich crisis held the attention of western Europe in 1609, the eyes of observers farther east were on Prague, the capital of Bohemia. That elective kingdom (which also included Silesia, Lusatia, and Moravia), together with Hungary, had come to the Habsburg family in 1526. At first they were ruled jointly with Austria by Ferdinand I (brother of Emperor Charles V), but after his death in 1564 the inheritance was divided into three portions: Alsace and Tyrol (known as “Further Austria”) went to one of his younger sons; Styria, Carinthia, and Carniola (known as “Inner Austria”) went to a second; only the remainder was left for his successor as emperor, Maximilian II.

By 1609 fragmentation had advanced even further: Maximilian’s eldest son, Rudolf II (emperor, 1576–1611), ruled only Bohemia; all the rest of his father’s territories had been acquired, the previous year, by a younger son, Matthias. The new ruler had come to power not through strength or talent, however, but by the exploitation of the religious divisions of his subjects. During the 1570s the Protestants of Austria, Bohemia, and Hungary had used their strength of numbers and control of local representative assemblies to force the Habsburgs to grant freedom of worship to their Protestant subjects. This was clearly against the cuius regio principle, and everyone knew it. In 1599 the ruler of Inner Austria, Archduke Ferdinand, began a campaign of forcible re-Catholicization among his subjects, which proved entirely successful. But, when Rudolf II launched the same policy in Hungary shortly afterward, there was a revolt, and the rebels offered the Hungarian crown to Matthias in return for guarantees of toleration. The Bohemians decided to exploit Rudolf’s temporary embarrassment by pressing him to grant similarly far-reaching concessions to the non-Catholic majority of that kingdom. The “Letter of Majesty” (Majestätsbrief) signed by Rudolf on July 9, 1609, granted full toleration to Protestants and created a standing committee of the Estates, known as “the Defensors,” to ensure that the settlement would be respected.

Rudolf II—a recluse who hid in a world of fantasy and alchemy in his Hradčany palace above Prague, a manic depressive who tried to take his own life on at least one occasion—proved to be incapable of keeping to the same policy for long. In 1611 he tried to revoke the Letter of Majesty and to depose the Defensors by sending a small Habsburg army into Prague, but a force of superior strength was mobilized against the invaders and the Estates resolved to depose Rudolf and offer their crown to Matthias. The emperor, broken in mind and body, died in January 1612. All his territories were then ruled by his brother, who also succeeded him as Holy Roman emperor later in the year. The alliance with the Protestant Estates that brought about Matthias’s elevation, however, did not long continue once he was in power. The new ruler sought to undo the concessions he had made, and he looked for support to his closest Habsburg relatives: his brother Albert, ruler of the Spanish Netherlands; his cousin Ferdinand, ruler of Inner Austria; and his nephew Philip III, king of Spain. All three, however, turned him down.

Albert had in 1609 succeeded in bringing the war between Spain and the Dutch Republic to a temporary close with the Twelve Years’ Truce. The last thing he wanted was to involve his ravaged country in supplying men and money to Vienna, perhaps provoking countermeasures from Protestants nearer home. Archduke Ferdinand, although willing to aid Matthias to uphold his authority (not least because he regarded himself as heir presumptive to the childless Matthias), was prevented from doing so by the outbreak of war between his Croatian subjects and the neighbouring republic of Venice (the Uskok War, 1615–18). Philip of Spain was also involved in war: in 1613–15 and 1616–17, Spanish forces in Lombardy fought the troops of the duke of Savoy over the succession to the childless duke of Mantua. Spain could therefore aid neither Matthias nor Ferdinand.

In 1617, however, papal diplomats secured a temporary settlement of the Mantuan question, and Spanish troops hastened to the aid of Ferdinand. Before long, Venice made overtures for peace, and the archduke was able to leave his capital at Graz in order to join Matthias. The emperor, old and infirm, was anxious to establish Ferdinand as his heir, and, in the autumn of 1617, the Estates of both Bohemia and Hungary were persuaded to recognize the archduke unconditionally as king-designate. On the strength of this, Ferdinand proceeded over the winter of 1617–18 to halt the concessions being made to Protestants. He created a council of regency for Bohemia that was overwhelmingly Catholic, and it soon began to censor works printed in Prague and to prevent non-Catholics from holding government office. More inflammatory still, the regents ordered Protestant worship to stop in towns on church lands (which they claimed were not included in the Letter of Majesty).

The Defensors created by the Letter of Majesty expressed strong objection to these measures and summoned the Estates of the realm to meet in May 1618. When the regents declared the meeting illegal, the Estates invaded the council chamber and threw two Catholic regents, together with their secretary, from the window. Next, a provisional government (known as the Directors) was created and a small army was raised.

Apart from the famous “defenestration,” the events in Prague in May 1618 were, superficially, little different from those in 1609 and 1611. Yet no 30-year struggle arose from those earlier crises. The crucial difference lay in the involvement of foreign powers: in 1609 and 1611 the Habsburgs, represented by Rudolf and Matthias, had given in to their subjects’ demands; in 1618, led by Ferdinand, they did not. At first his defiant stance achieved nothing, for the army of the rebels expelled loyal troops from almost every part of the kingdom while their diplomats secured declarations of support from Silesia, Lusatia, and Upper Austria almost at once and from Moravia and Lower Austria shortly afterward. In May 1619 the rebel army even laid siege to Ferdinand in Vienna. Within weeks, however, they were forced to withdraw because a major Spanish army, partly financed by the pope, invaded Bohemia.

The appearance of Spanish troops and papal gold in eastern Europe immediately reawakened the fears of the Protestant rulers of the empire. To the government of Philip III, led by the former ambassador in Vienna, Don Balthasar de Zúñiga, the choice had seemed clear: “Your Majesty should consider,” wrote one minister, “which will be of the greater service to you: the loss of these provinces [to the house of Habsburg], or the dispatch of an army of 15 to 20 thousand men to settle the matter.” Seen in these terms, Spain could scarcely avoid military intervention in favour of Ferdinand; but to Protestant observers the logic of Spanish intervention seemed aggressive rather than defensive. Dudley Carleton, the English ambassador to the Dutch Republic, observed that the new emperor “flatters himself with prophesies of extirpating the Reformed religion and restoring the Roman church to the ancient greatness” and accurately predicted that, if the Protestant cause were to be “neglected and by consequence suppressed, the Protestant princes adjoining [Bohemia] are like to bear the burden of a victorious army.”

This same argument carried weight with the director of the Protestant Union, Frederick V of the Palatinate, parts of whose territories adjoined Bohemia. So, when in the summer of 1619 the Bohemians deposed Ferdinand and offered the crown to Frederick, he was favourably disposed. Some of the elector’s advisers favoured rejecting this offer, since “acceptance would surely begin a general religious war”; but others pointed out that such a war was inevitable anyway when the Twelve Years’ Truce between Spain and the Dutch Republic expired in April 1621 and argued that allowing the Bohemian cause to fail would merely ensure that the conflict in the Netherlands would be resolved in Spain’s favour later, making a concerted Habsburg attack on the Protestants of the empire both ineluctable and irresistible.

Frederick accepted the Bohemian crown and in so doing rekindled the worst fears of the German Catholics. The Catholic League was re-created, and in December 1619 its leaders authorized the levy of an army of 25,000 men to be used as Maximilian of Bavaria thought fit. At the same time, Philip III and Archduke Albert each promised to send a new army into Germany to assist Ferdinand (who had succeeded the late Matthias as Holy Roman emperor). The crisis was now apparent, and, as the Palatine diplomat Count John Albert Solms warned his master,

If it is true that the Bohemians are about to depose Ferdinand and elect another king, let everyone prepare at once for a war lasting twenty, thirty or forty years. The Spaniards and the House of Austria will deploy all their worldly goods to recover Bohemia.

The underlying cause for the outbreak of a war that would last 30 years was thus the pathological fear of a Catholic conspiracy among the Protestants and the equally entrenched suspicion of a Protestant conspiracy among the Catholics. As a Bohemian noblewoman, Polyxena Lobkovic, perceptively observed from the vantage point of Prague: “Things are now swiftly coming to the pass where either the papists will settle their score with the Protestants, or the Protestants with the papists.”