The Swedish invasion of the Holy Roman Empire or the Swedish Intervention in the Thirty Years' War is a historically accepted division of the Thirty Years' War. It was a military conflict that took place between 1630 and 1635, during the course of the Thirty Years' War. It was a major turning point of the war: the Protestant cause, previously on the verge of defeat, won several major victories and changed the direction of the War. The Habsburg-Catholic coalition, previously in the ascendant, was significantly weakened as a result of the gains the Protestant cause made. It is sometimes considered to be an independent conflict by historians.
Following the Edict of Restitution by Emperor Ferdinand II on the height of his and the Catholic League's military success in 1629, Protestantism in the Holy Roman Empire was seriously threatened. In July 1630, King Gustav II Adolf of Sweden landed in the Duchy of Pomerania to intervene in favor of the German Protestants. Although he was killed in battle at Lützen, southwest of Leipzig, the Swedish armies achieved several victories against their Catholic enemies. However, the decisive defeat at Nördlingen in 1634 threatened continuing Swedish participation in the war. In consequence, the Emperor made peace with most of his German opponents in the Peace of Pragueessentially revoking the Edict of Restitutionwhile France directly intervened against him to prevent the Habsburg dynasty from gaining too much power at its eastern border.
Sweden was able to fight on until the Peace of Westphalia in 1648 in which the Emperor was forced to accept the "German liberties" of the Imperial Estates and Sweden obtained Western Pomerania as an Imperial Estate.
Religious and political background: The Bohemian Revolt
The Thirty Years' War was a religious conflict between Protestants and Catholics in Germany. It originated in the co-mingling of politics and religion that was common in Europe at the time. Its distal causes reside in the previous century, at the political-religious settlement of the Holy Roman Empire known as the Peace of Augsburg. The peace was an agreement between Charles V, Holy Roman Emperor and the Protestant powers of the Holy Roman Empire in the 16th century. It established the legitimacy of Lutheranism in Germany and allowed Dukes and high lords to determine the faith of their fiefdom as well as to expel non-conforming subjects from their territory, the principle known as Cuius regio, eius religio. Additionally, it permitted subjects of a different religion to peaceably move to land where their practices would be recognized and respected. There were also clauses in relation to ecclesiastical lords. When prelates who ruled an ecclesiastical fiefdom converted, the expectation was placed upon them to resign their temporal privileges. Some of these treaty stipulations would be violated on various occasions, as was the case with Gebhard Truchsess von Waldburg, Archbishop-Elector of Cologne. Despite various attempts to violate the provisions in the Peace of Augsburg no general European or German conflagration would erupt as a result of the violations. At the end of the conflicts, it was agreed that the provisions of the Peace of Augsburg would once again be adhered to. "All that the Lutheran church gained by the Peace of Augsburg was toleration; all that the [Roman] church conceded was a sacrifice to necessity, not an offering to justice" says one historian. However, the Peace of Augsburg could never be anything but a temporary cessation of hostilities. Its provisions contained an addendum that declared that it would only become active without reservation upon the meeting of a general council and a final attempt at the reunion of the two confessions. There was no reason to believe these would ever happen unless the Lutherans were forced to do so.
Although genuine ideological differences did drive German Princes to convert, the primary motivation of many was often the acquisition of easy riches and territory at the expense of their defenceless Catholic neighbours and subjects. Princes would convert on the grounds that they would be empowered to seize precious land and property from the Roman Catholic Church, and turn that wealth to their own enrichment.