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The Thirty Years’ War Began 400 Years Ago – And We’re All Living In The World It Created

This year marks the centenary of the end of the First World War, but that’s not the only major commemoration on our current calendars. In fact, the year 2018 also marks the anniversary of two interconnected events that changed European and world history forever. These are the 400th anniversary of the start of the Thirty Years’ War, and the 370th anniversary of the Treaties that ended it – the famous Peace of Westphalia. The conflict counts among the bloodiest in history, and its astounding death toll haunted Europe for generations. The Peace created the international system as we know it.

The Road To War

Banner of the Holy Roman Empire thirty
Banner of the Holy Roman Empire

The Thirty Years’ War began when three representatives of the Holy Roman Empire were thrown out the window of the royal castle in Prague in 1618, sparking a continent-wide religious conflict. The following thirty years tore the heart out of Europe, killing nearly a quarter of the entire German population and devastating Central Europe to such an extent that many towns and regions never recovered. All the major European powers apart from Russia were heavily involved and, while each country started out with rational war aims, the battles rapidly spiralled out of control, with armies giving way to marauding bands of starving soldiers, spreading plague and murder.

The Thirty Years’ War can be roughly divided into four parts: the outbreak of hostilities with the Bohemian War, the Danish intervention, the Swedish intervention, and the French intervention. To begin, some of the issues that lay behind it must first be understood. The road to war began with a local conflict, internal to the Holy Roman Empire, which then exploded into a massive war that would lead to millions of deaths and the destruction of hundreds of villages and cities. By the war’s end, mostly Swedish and French forces could move around the Germanies almost at will, taking and burning what they wanted. The tides of war led to the quick decentralization of the Holy Roman Empire, and to a peace of great historical significance.

Christianity Divided

An elderly Carl V
An elderly Carl V

The roots of the war are grounded in the Peace of Augsburg, established in 1555. Charles V (Holy Roman Emperor/Charles I of Spain) made abortive efforts during 1540-1541 to enforce a compromise agreement between the Protestants and the Catholics within the Holy Roman Empire, which threatened to tear the realm apart. When these and other conciliar efforts failed, he turned to military solutions. In 1547, imperial armies crushed the Protestant Schmalkaldic League. The emperor established puppet rulers in Saxony and Hesse and issued an imperial law, the Augsburg Interim, which commanded Protestants everywhere to readopt Catholic beliefs and practices. The effort came to naught: the Reformation was too entrenched by 1547 to be ended even by brute force. Charles, already weary from three decades of war, relented when he was confronted by fierce Protestant resistance.

In September 1555, the treaty made the division of Christendom permanent. This agreement recognised in law what had already been established in practice: “cuius regio, eius religio,” meaning that the ruler of a land would determine the religion of the land. Lutherans were permitted to retain all church lands that had been forcibly seized before 1552. Those who were discontented with the religion of their region were permitted to migrate to another.

Flag of the Catholic League
Flag of the Catholic League

It is worth noting that Calvinism was not recognised as a legal form of Christian belief and practice by the Peace of Augsburg. However, Calvinists remained determined not only to secure their right to worship publicly as they pleased but also to shape society according to their own religious convictions. They reacted by orchestrating national revolutions throughout northern Europe.

In 1609, Maximilian, Duke of Bavaria (1573-1651), organised a Catholic League to counter a new Protestant alliance that had been formed by the Calvinist Elector Palatine, Frederick IV (r. 1583-1610). When the League fielded a great army under the command of Johann Tserclaes, Count of Tilly (1559-1651), the stage was set, internally and internationally, for the Thirty Years’ War, the worst European catastrophe since the Black Death.

Protestants Take Up Arms Against The Empire

The defenestration of Prague became the signal for a general rebellion in predominantly Protestant Bohemia. It started in Prague but soon spread to the other territories encompassing the Crown of Bohemia, stretching into Austrian territory. In the summer of 1618, the revolt had already gained footholds in Silesia, Lusatia and Upper Austria. The first actual battles in the Thirty Years’ War took place near the city of Pilsen (modern Plzeň, Czechia) where many Catholics had taken refuge. To stop the Catholics from receiving reinforcements, the Bohemian rebels under Ernst von Mansfeld marched towards Pilsen, and the siege thus began in September. Like the first battle, the first siege also ended with an overwhelming victory for the Protestants.

The Winter King on the Retreat

Painting celebrating the Catholic victory, by Antonín Stevens
Painting celebrating the Catholic victory, by Antonín Stevens

The victory gave the Bohemians an upper hand, but they had to strike while the iron was hot. To do this, they had to gather as many allies as possible and strike into the heartland of the Habsburgs in Austria. However, few neighbours were willing to risk a European war to aid the Bohemians. Only one Western European State, little Savoy, supplied the Bohemians with economic assistance – but it was not enough. After constant fighting that stretched for years, the Bohemians were eventually handed a crushing defeat at the Battle of White Mountain.

For the Bohemians, this battle was a disaster. Their lands were returned to the Catholics, and the Jesuits took control of the University of Prague. Countless people were executed as traitors and rebels, hundreds of thousands of people fled. Bohemia would then remain a stable part of the Habsburg Empire for three centuries.

While the Habsburgs were under assault from several directions, the Transylvanians under Gábor Bethlen took the opportunity to invade Hungary from the East. The crisis continued to escalate: the Swiss lent aid to rebels in Northern Italy, and the Palatine and the Bohemians also pushed hard from several directions.
By 1621, however, the Habsburgs were victorious everywhere. Order had been restored in Bohemia, Hungary, and Valtellina in Italy. In the Palatine, Frederick V (dubbed the “Winter King”) lost fortification after fortification. To outside eyes, the conflict looked all but over. But nothing could be further from the truth.

A General European War: Danish Intervention

Emperor Ferdinand II and his advisors bear the brunt of responsibility for the continuation of the war. A compromise could have been reached if they had  been satisfied with depriving Frederick V of the Bohemian Crown, but seeing the prospect of a complete and total victory, the Habsburgs fought on, persuading Frederick V to carry on.

Meanwhile, seeing the triumphs of the Catholics, Spain saw an opportunity to settle its score with the Dutch. With Northern Italy and the Palatine firmly under Catholic Habsburg control, the road to the Netherlands lay open. The instigators of this war were the Count-Duke of Olivares, Ferdinand II; Cardinal Richelieu of France, and Gustav II Adolf of Sweden. They were responsible for prolonging the conflict.

Christian IV of Denmark on the ship Trefoldigheden in the battle of Kolberger-Heide 1644
Christian IV of Denmark on the ship Trefoldigheden in the battle of Kolberger-Heide 1644

When Christian IV of Denmark intervened in the Thirty Years’ War, he was at the peak of his power. Income from the ransom of Älvsborgs Castle and the Sound Dues made it easy for him to cough up money for military expeditions. He also had personal reasons for intervening. He had hoped that a quick and decisive strike into Germany would land him the territories of Bremen, Verden, and Schwerin for his two sons.

Emperor Ferdinand II secured the assistance of Albrecht von Wallenstein (1583-1634), who raised an independent army of 50,000. The combined forces of Wallenstein and Tilly defeated Christian IV in 1626, and then proceeded to occupy the duchy of Holstein. The Treaty of Lubeck, signed in 1629, restored Holstein to Denmark, but the Danish king pledged not to intervene further in German affairs. The Danish period of the war, like the Bohemian period, thus ended with a Habsburg and Catholic victory. Protestants everywhere were alarmed by the Catholic victories. The Emperor’s triumphs endangered the independence of the German princes, while the French Bourbons were concerned about the growth of Habsburg power.

Turning Point: Swedish Intervention

Bust of King Gustav Adolph on campus at Gustavus Adolphus College in Minnesota
Bust of King Gustav Adolph on campus at Gustavus Adolphus College in Minnesota

King Gustav II Adolf (r. 1611 – 1632) of Sweden became the new leader of the Protestant cause. In the summer of 1630, the Swedes made landfall in Germany. This marked one of the turning points of the Thirty Years’ War, but it must be emphasized that Swedish intervention was not a foregone conclusion. By 1630, the war had raged for twelve years. Denmark had been swiftly defeated upon intervening.
It would have been easy for Gustav II Adolf and his Lord High Chancellor, Axel Oxenstierna, to stay neutral and focus on the campaign they really burned for: fighting against Sigismund III Wasa of Poland.

As the name implies, Sigismund was of Swedish origin. He was the son of the Swedish king Johan III, and of the Polish princess Catherine Jagiellon, but he lost the crown. However, he still planned to reclaim Sweden. Gustav II Adolf could have focused on ending this threat, but chose instead to steer Sweden towards the Protestant cause, and against Germany.


Sweden’s intervention also presented a useful convergence of interests with France, which remained embroiled in its own goal of limiting Habsburg power and agreed to provide Gustav II Adolf with an annual subsidy of 400,000 talers to maintain an army in the conflict. After consolidating his position across the Baltic, the Swedish king led a stunningly successful campaign, culminating in the battle at Breitenfeld in 1631. This battle destroyed an Imperial army under the command of General Tilly and gave Gustav II Adolf a dominant position in northern Germany, inflicting the first massive defeat to the Imperial forces. He then consolidated his position and conducted a lightning campaign to wrest much of present-day Germany from Imperial control. His success, however, met an abrupt end with his death at Lützen in 1632, having fought Wallenstein’s army to a draw in the process.

Thirty Years And No Sign of Peace

Panoramic view of Prague Castle
Panoramic view of Prague Castle

Three years later, in 1635, the Thirty Years’ War could well have ended, thanks to the Peace of Prague. This treaty was signed by Ferdinand II and the Elector of Saxony, Johann Georg I. The Peace was important because Saxony was one of the largest and most powerful of the German Protestant states, and their support for Sweden had been instrumental in the efforts of the Swedish to build a network of alliances across Germany.

In 1631 and 1632, Sweden saw great victories and gains, and to a degree this continued in 1633 and 1634 even after the Battle of Lützen. All of this was swept away inthe Battle of Nördlingen, a true disaster for Swedish forces. Without active support from Richelieu, king Louis XIII’s chief minister, the Swedish could have been smacked back across the Baltic Sea, and the officials of the Holy Roman Empire hoped that 1635 would be the year that resulted in peace and German unity. Instead, the exact opposite happened: 1635 became the watershed that expanded the Thirty Years’ War to its final phase, when France actively got involved in the fighting.

The many theaters of the Thirty Years’ War – the Netherlands, Italy, and Germany – were intertwined, causing the war to spread with no peace in sight. Ferdinand II had viewed the Peace of Prague as a compromise: the fortunes of war could change rapidly as evident from the Battle of Breitingen and then from the Battle of Nördlingen. However, Ferdinand II now had an excellent opportunity to restore much of the positions lost to Gustav II Adolf of Sweden. This required the sacrifice of certain principles – the alternative was to go through a new round of war against all the Protestant states and Sweden, after all. Thus, Ferdinand abandoned many of the religious edicts that had propelled German anger into a full-blown conflict. He reinstated “cuius regio, eius religio,” paving the way for Protestant rulers to practice their faith in the open. This in turn meant that in 1635, the Thirty Years’ War lost the final claim it had to being a war of religion.

Spiralling Out of Control: French Intervention

Cardinal Richelieu by Robert Nanteuil
Cardinal Richelieu by Robert Nanteuil

France’s official entry in the war followed a long history of rivalry against the Habsburgs. Richelieu and Louis XIII had chosen a side long before 1635, in line with the traditional anti-Habsburg politics of France. They had supported the Netherlands and Sweden financially, and they had intervened against the Habsburgs directly on several occasions as evident from the Mantuan Succession War. Furthermore, Richelieu had strengthened France’s political situation by creating allied buffer States; the most obvious example was the Duchy of Savoy. The Savoyan rulers, however, had continually shown that they would rather make deals with the Habsburgs than bow down to Paris. By the mid-1630’s, though, the Duchy of Savoy was essentially a French satellite State whose interests aligned with Richelieu’s.

Another example is the German Archbishopric of Trier which accepted protection from France, granting Paris access to three strategically important fortresses– Koblenz, Ehrenbreitstein, and Phillipsburg.  A final example is Lothringen (modern-day Lorraine), then part of the Holy Roman Empire. The Duke of Lothringen, Charles IV, had a habit of cutting deals with the Habsburgs and broke promises made to France; thus allowing the Habsburgs to occupy strategic sites along the border to France. Finally, in 1633, this caused the French to invade the duchy and occupy it. By achieving all of this pre-1635, Richelieu had prepared for the French intervention, which aimed to break the Habsburg encirclement of France.

Despite many failures and disappointments during the first few years, especially when Spanish and Austrian troops came dangerously close to Paris after beating back the French in the Netherlands and from the Rhine, French intervention kept the war going. However, neither the Habsburgs nor the French alliance were able to strike a decisive blow until 1640, where the situation favoured the Swedish, the French, and their allies. While they were still unable defeat the Habsburgs, they kept up the advantage until the Peace of Westphalia in 1648.

The New Power Balance

The treaties that comprised the Peace of Westphalia had important ramifications for Europe. The end of the war cemented France as the premier land power on the continent, a position it would keep until the defeat in the Napoleonic wars; and it consecrated Sweden as a European Great Power, a status that Stockholm would keep until the end of the Great Northern War.

The Ratification of the Treaty of Westphalia, 15 May 1648 (1648)
The Ratification of the Treaty of Westphalia, 15 May 1648 (1648)

For Austria, two important things came from the Peace of Westphalia. Firstly, Cardinal Jules Mazarin (Chief Minister of the French King) was adamant in his demands that the Habsburgs of Austria be forced to cut ties with the Spanish Habsburgs, leaving Spain out of the peace treaty. France wanted Philip IV of Spain to lose all Austrian support. Ferdinand III of Austria was therefore forced to solemnly swear to withhold any and all aid to his Pyrenean relatives.

The Austrian ruler was reluctant, and for good reason. The alliance between Madrid and Vienna was old and connected the Habsburg house. However, during the Autumn of 1648, Ferdinand was forced to agree to the terms. The Spanish defeat at the Battle of Lens, and the Swedish conquest of half of Prague made continued warfare look extremely grim for Austria.  Another year of war could lead to even greater demands from the Swedish-French alliance, and so, Ferdinand grudgingly accepted.

Secondly, the peace established that the German rulers of the various duchies, kingdoms, counties, and cities throughout Germany were given a large degree of autonomy from the Holy Roman Emperor. However, no longer anchored to the warlike preferences of the Spaniards, and with fewer means to directly interfere in German politics, Austria was now able to pursue her true destiny: the East, where the dangerous behemoth known as the Ottoman Empire stood not far away from Vienna itself. In this way, Westphalia turned out to be a surprising blessing in disguise for Austria, allowing the Empire to increase its territory and consolidate its status as a Great Power over the next two centuries.

The Treaties that Changed the World

Holy Roman Empire in 1648.
Holy Roman Empire in 1648.

The legacy of Westphalia, however, goes well beyond the peace itself and the new order it brought to Europe. The Treaties established new legal principles that had major ramifications for the international order. The key novelty is the rejection of the universalistic ideas of the Middle Ages: the Church and the Empire, and their respective claims to ecumenism.

By effectively outlawing crusades between European nations, and establishing each country’s right to pick a religion without outside interference, Westphalia defined sovereignty and put the nation-State at the center of the political system for the very first time. In the post-Westphalian world, there is no authority that ranks above sovereign States, save for those that States themselves recognize as superior through a treaty. This is known as Westphalian Sovereignty, and is the basic framework that defines the entirety of international relations, and remains a core mechanic of international law to this day.

The norm-based European order that arose from the Thirty Years’ War would eventually grow in complexity and normativity, and would spread to the rest of the world in the wake of European imperialism and global preeminence during the two following centuries. With religious tolerance codified on a legal level, and States recognized as the primary agents of the international system, European diplomacy began to move towards the so-called peace conference system: the creation of fora for States to interact and resolve disputes. This system would peak during the European Concert, and the current United Nations are built on the strengths and weaknesses displayed by the conference system over the centuries.

The Thirty Years’ War began as the largest religious war in European history, but the Peace that ended it became the turning point of international relations. At Westphalia, European countries first plotted their course towards the international system as we know it today.

Did you enjoy reading this article? You may also like  On this day in 1933: Adolf Hitler becomes Chancellor of the German Reich or On this day in 1741: the War of Austrian Succession.


Tullio Pontecorvo

Student of political science and international relations, co-founder of My Country? Europe. Aspiring sci-fi author. Believes shooting aliens in the face to be the ultimate form of gaming.

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