The Habsburgs, meanwhile, were hampered in their advancement of the Roman Catholic cause by the growing mental incapacity of Rudolf II; indeed, much of the direction of affairs was transferred to his brother Matthias, who eventually succeeded him in 1612. A more serious undermining of Habsburg imperial power occurred in the dynastic lands. Rigorous Catholic reform occasioned peasant uprisings in Austria and resistance by nobles in Hungary and Bohemia (where Calvinism had made inroads among the ruling classes). In Hungary a nationalist party under Bocskay István forged an alliance with Lutheran princes and obtained support from the Turks. In Bohemia in 1609 the estates extracted from the emperor a guarantee of religious freedom, the so-called Letter of Majesty.
At about the same time, the city of Donauwörth was occupied by Bavarian troops, since the emperor had empowered Duke Maximilian of Bavaria to “protect” the Roman Catholic minority there. Seeing this “Donauwörth incident” as a straw in the wind, Lutheran and Calvinist rulers formed a Protestant Union (1608), the answer to which was the Catholic League (1609), headed by Maximilian, the most resolute Catholic prince in the empire. Each party organized an army and allied itself with foreign powers, the Protestants with France and Bohemia, the Catholics with Spain. In this way the German struggle was both militarized and internationalized.
General war nearly broke out in 1609–10 over the Jülich-Cleves succession crisis. When the Roman Catholic ruler of these counties, which formed the strategically most important block of territories on the lower Rhine, died without an heir, two Protestant claimants occupied his lands, aided not only by the German Protestant Union but also by France and England; they were, however, militantly opposed by Spain and the emperor. The assassination of Henry IV of France, who had been about to launch an invasion in support of the Protestant claimants, defused the crisis in 1610.
Peace was preserved, although not for long. The Bohemian situation finally precipitated the war. Because neither Rudolf II nor Matthias had left legitimate heirs, the governance of the Habsburg dynastic lands fell to Archduke Ferdinand of Styria (later Emperor Ferdinand II), a ruthless counterreformer who reduced the religious liberties granted to Bohemians under the Letter of Majesty. In response, the Bohemian estates in May 1618 mounted a protest in Hradčany (the Prague Castle district), which prompted a militant faction of deputies to throw two imperial councillors from a castle window (defenestration being a traditional Bohemian gesture of defiance). In response to this event, which came to be known as the Defenestration of Prague, Ferdinand now prepared military action, while the Bohemian estates elected a Calvinist, Frederick V of the Palatinate, to be their king. As the alliances fell into place on each side, the stage was set for the sequence of large-scale military actions that constituted the Thirty Years’ War. The Thirty Years’ War and the Peace of Westphalia
The Bohemian problem was resolved swiftly. Two Roman Catholic armies, the emperor’s and the League’s, converged on the kingdom, routing Frederick at the White Mountain in November 1620 and replacing the regime of the estates in Bohemia with a system of “confessional absolutism” based on rigid Catholic conformity and political authoritarianism. At the same time, the Palatinate was conquered by Spanish and Bavarian troops, and the electoral title was transferred to Maximilian of Bavaria in 1623. In the Palatinate, too, the Counter-Reformation sought to bring Protestantism to an end. As the war spread into Hesse and Westphalia and as Spain resumed its attack on the Netherlands, Catholic forces seemed near triumph. This prospect, however, renewed the old fear, as in the time of Charles V, of Habsburg hegemony; an anti-Habsburg alliance was therefore forged by France (where Cardinal Richelieu took charge of affairs in 1624), England (whose ruler, James I, was father-in-law to the deposed Frederick V), the Netherlands, and Denmark (whose Protestant king, Christian IV, had extensive territorial interests in northern Germany, now threatened by Catholic armies). In 1625 Christian IV commenced hostilities. He was opposed by a much-enlarged imperial force under the war’s most flamboyant figure, Albrecht von Wallenstein, a military entrepreneur with a gift for mobilizing troops and supplying them through ruthless plundering. Wallenstein’s plan was to wreck Dutch and English commerce in the Baltic by subduing all of northern Germany and by dislodging the Swedish king, Gustav II Adolf, from Prussia (taken in the course of Sweden’s war against Poland). By 1628 much of this objective was realized. Christian IV had been decisively defeated in 1626 in the Battle of Lutter am Barenberge and forced to make peace in 1629. To crown these successes, Ferdinand II issued in March of that year the Edict of Restitution, by which Protestant rulers were to restore to the church more than 500 bishoprics, monasteries, abbeys, and other ecclesiastical properties secularized since 1552.
But this impressive strengthening of the sovereign’s power in the empire brought his foreign and domestic enemies together once more, the latter including now not only Protestants but also Roman Catholic estates concerned about their liberties. Subsidized by the Dutch and French and allied with Saxony, Sweden entered the conflict in 1630, winning commanding victories at Breitenfeld (1631) and Lützen (1632) but suffering defeat at Nördlingen in 1634. This phase of the war was marked by unprecedented brutality; for example, in 1631, imperial troops massacred two-thirds of the population of Magdeburg, a city of 20,000 that had withstood a long siege.
A way out of the long conflict appeared in 1635 when Saxony, Brandenburg, and other Protestant states seeking to end foreign intervention joined the emperor in the Peace of Prague, which included the revocation of the Edict of Restitution. But in the war’s final phase, France, seeking to forestall Spanish preponderance on the Continent, offered large subsidies to Sweden and to German princes to enable them to fight on. Combined Swedish-French campaigns commenced in 1638, and a decade later foreign armies operated as far south as Bavaria, while the French held Lorraine and Alsace, which was important to France to prevent construction of a Spanish land bridge from the Netherlands to Italy.
By then most belligerents were exhausted. Several German princes had quit the war. Since 1644, representatives of the powers had been talking about terms, although military operations continued in hopes of improving bargaining positions. In 1648, finally, treaties were signed in Münster and Osnabrück (both in Westphalia) by agents of the emperor, the German states, Sweden, and France as well as between Spain and the Netherlands. Fighting continued for some years—France and Spain did not conclude peace until 1659—but the war was at last winding down.
The Peace of Westphalia brought territorial gains to Sweden and France, awarded an electoral seat to Bavaria, and secured for Protestant rulers the church properties they had confiscated, based on the status quo of 1624. More important, it brought Calvinists into the religious settlement and established the independence of the Netherlands from Spain and of Switzerland from the empire. Most significant of all, it guaranteed the nearly unlimited territorial sovereignty of German princes, bringing to an end the last effort (until the 19th century) to centralize power in the empire. In this way the Peace of Westphalia sealed the fragmentation of the Holy Roman Empire into hundreds of autonomous political entities, most of them small. At the same time, it brought to an end the last major conflict in continental Europe in which religion was a central issue; indeed, the war itself had demonstrated that reason of state was a stronger determinant of policy than faith. In declaring the religious situation fixed as of 1624, the treaty mandated that, if a prince converted, his land no longer converted with him. Religious pluralism and—albeit grudgingly—coexistence were now the norm.