It has been famously pointed out that the Holy Roman Empire was neither holy, nor Roman, but it was also not an empire in the sense people expect when hearing the term. In theory, the emperor was the highest prince in Christendom, and his dominion extended the length and breadth of Western Europe. The empire had been created by the papacy in 801 when Pope Leo III famously crowned the supposedly unwitting Charlemagne in Saint Peter’s Basilica, intending to recreate the Western Roman Empire. In truth, the imperial power did not extend beyond central Europe, which by the beginning of the 16th century included Germany, northern Italy, and the Netherlands. Even in these lands, however, the emperor struggled to command obedience.

Meanwhile, The attempt in 1588 by the Spanish Armada to subjugate the Netherlands and England by invading England was defeated, and in 1609, with both sides totally exhausted, fighting was suspended during a 12-year truce made between the new Spanish king and the Dutch Republic. However, attempts to secure a more permanent peace floundered on the question of religious freedom for Catholics in the United Provinces and for Protestants in the southern provinces. Trade conflicts also proved impossible to resolve, and the truce was broken briefly in 1609 and 1614 over the issue of succession in the United Duchies of Julich-Cleves-Berg. This large collection of territories in northwestern Germany bordered the Netherlands, and both Catholic and Protestant powers were eager to gain control when its duke died without an obvious heir. Anxious to prevent a Habsburg presence on its western frontiers, the United Provinces joined with Protestant princes and France against the Habsburg Holy Roman Emperor, Spain, and a coalition of German Catholic states. After the Treaty of Xanten was agreed to on November 12, 1614, the territories were divided between the Catholic Count Palatine of Neuberg and the Protestant Elector of Brandenburg, an arrangement that satisfied neither side and aggravated Protestant and Catholic tensions. Four years later, the whole of Germany was set aflame when Protestants in Bohemia expelled representatives of Emperor Matthias II, who had briefly been governor of the Netherlands in 1578.

The ensuing Thirty Years' War was one of the most horrific conflicts in history, and though it is widely viewed as a religious struggle, that was only part of the complicated war. Calvinists and Lutherans did not get along, and both persecuted some of the more radical Anabaptist sects. At the same time, one major motivation behind the war was Holy Roman Emperor Ferdinand II’s determination to rule all of the empire and not be just a figurehead. There were struggles between rulers and their estates over power, and Catholic France later entered the war on the side of the Protestants in order to counter the Habsburgs’ power.

The Battle of Breitenfeld, fought in September 1631, was one of the most decisive moments of the war. It was the first major Protestant victory and widely considered the crowning achievement of Swedish King Gustavus Adolphus’ military career. Through his establishment of communication and supply lines at strategic points across the Baltic Sea, the securing of Protestant alliances, and his use of combined arms, amongst his other trademark techniques, the Swedish forces, against all odds, defeated their rivals. Such was the devastation inflicted upon their opponents that the Count of Tilly, the chief commander of the Catholic League's armies, had no other choice but to retreat. 6,000 or so Catholic soldiers were captured, many of them later incorporated into the Protestant forces. Whatever remained of the survivors vanished into the dark of the night.