Overview

The Thirty Years’ War was a series of wars in Central Europe between 1618 and 1648. It was one of the longest and most destructive conflicts in European history, resulting in millions of casualties.

Initially a war between various Protestant and Catholic states in the fragmented Holy Roman Empire, it gradually developed into a more general conflict involving most of the great powers. These states employed relatively large mercenary armies, and the war became less about religion and more of a continuation of the France-Habsburg rivalry for European political pre-eminence. In the 17th century, religious beliefs and practices were a much larger influence on an average European. In that era, almost everyone was vested on one side of the dispute or another.

The war began when the newly elected Holy Roman Emperor, Ferdinand II, tried to impose religious uniformity on his domains, forcing Roman Catholicism on its peoples. The northern Protestant states, angered by the violation of their rights to choose granted in the Peace of Augsburg, banded together to form the Protestant Union. Ferdinand II was a devout Roman Catholic and relatively intolerant when compared to his predecessor, Rudolf II. His policies were considered heavily pro-Catholic.

The Holy Roman Empire

The Holy Roman Empire was a fragmented collection of largely independent states. The position of the Holy Roman Emperor was mainly titular, but the emperors, from the House of Habsburg, also directly ruled a large portion of imperial territory (lands of the Archduchy of Austria and the Kingdom of Bohemia), as well as the Kingdom of Hungary. The Austrian domain was thus a major European power in its own right, ruling over some eight million subjects. Another branch of the House of Habsburg ruled over Spain and its empire, which included the Spanish Netherlands, southern Italy, the Philippines, and most of the Americas. In addition to Habsburg lands, the Holy Roman Empire contained several regional powers, such as the Duchy of Bavaria, the Electorate of Saxony, the Margraviate of Brandenburg, the Electorate of the Palatinate, Landgraviate of Hesse, the Archbishopric of Trier, and the Free Imperial City of Nuremberg.

Peace of Augsburg

After the Protestant Reformation, these independent states became divided between Catholic and Protestant rulership, giving rise to conflict. The Peace of Augsburg (1555), signed by Charles V, Holy Roman Emperor, ended the war between German Lutherans and Catholics. The Peace established the principle Cuius regio, eius religio (“Whose realm, his religion”), which allowed Holy Roman Empire state princes to select either Lutheranism or Catholicism within the domains they controlled, ultimately reaffirming the independence they had over their states. Subjects, citizens, or residents who did not wish to conform to a prince’s choice were given a period in which they were free to emigrate to different regions in which their desired religion had been accepted.

Although the Peace of Augsburg created a temporary end to hostilities, it did not resolve the underlying religious conflict, which was made yet more complex by the spread of Calvinism throughout Germany in the years that followed. This added a third major faith to the region, but its position was not recognized in any way by the Augsburg terms, to which only Catholicism and Lutheranism were parties.

Religion in the Holy Roman Empire, 1618

Religion in the Holy Roman Empire on the eve of the Thirty Years’ War. Blues indicate Catholic regions and red/orange indicate Protestant (including Lutheran, Calvinist, Hussite, and Reform).

German map of religious demographics in the Holy Roman Empire before the outbreak of the Thirty Years’ War.

Tension Mount

Religious tensions remained strong throughout the second half of the 16th century. The Peace of Augsburg began to unravel—some converted bishops refused to give up their bishoprics, and certain Habsburg and other Catholic rulers of the Holy Roman Empire and Spain sought to restore the power of Catholicism in the region. This was evident from the Cologne War (1583–1588), in which a conflict ensued when the prince-archbishop of the city, Gebhard Truchsess von Waldburg, converted to Calvinism. As he was an imperial elector, this could have produced a Protestant majority in the college that elected the Holy Roman Emperor, a position that Catholics had always held.

At the beginning of the 17th century, the Rhine lands and those south to the Danube were largely Catholic, while the north was dominated by Lutherans, and certain other areas, such as west-central Germany, Switzerland, and the Netherlands, were dominated by Calvins. Minorities of each creed existed almost everywhere, however. In some lordships and cities, the numbers of Calvinists, Catholics, and Lutherans were approximately equal.

Much to the consternation of their Spanish ruling cousins, the Habsburg emperors who followed Charles V (especially Ferdinand I and Maximilian II, but also Rudolf II and his successor, Matthias) were content to allow the princes of the empire to choose their own religious policies. These rulers avoided religious wars within the empire by allowing the different Christian faiths to spread without coercion. This angered those who sought religious uniformity. Meanwhile, Sweden and Denmark, both Lutheran kingdoms, sought to assist the Protestant cause in the Empire, and wanted to gain political and economic influence there as well.

By 1617, it was apparent that Matthias, Holy Roman Emperor and King of Bohemia, would die without an heir, with his lands going to his nearest male relative, his cousin Archduke Ferdinand II of Austria, heir-apparent and Crown Prince of Bohemia.

War Breaks Out

Ferdinand II, educated by the Jesuits, was a staunch Catholic who wanted to impose religious uniformity on his lands. This made him highly unpopular in Protestant Bohemia. The population’s sentiments notwithstanding, the added insult of the nobility’s rejection of Ferdinand, who had been elected Bohemian Crown Prince in 1617, triggered the Thirty Years’ War in 1618, when his representatives were thrown out of a window and seriously injured. The so-called Defenestration of Prague provoked open revolt in Bohemia, which had powerful foreign allies. Ferdinand was upset by this calculated insult, but his intolerant policies in his own lands had left him in a weak position. The Habsburg cause in the next few years would seem to suffer unrecoverable reverses. The Protestant cause seemed to wax toward a quick overall victory.

The war can be divided into four major phases: The Bohemian Revolt, the Danish intervention, the Swedish intervention, and the French intervention.

Ferdinand II

Ferdinand II, Holy Roman Emperor and King of Bohemia, whose aim, as a zealous Catholic, was to restore Catholicism as the only religion in the empire and suppress Protestantism, and whose actions helped precipitate the Thirty Years’ War.