How a surprise Swedish invasion ended Denmark’s dominance over the Baltic Sea
In 1643, Sweden launched a lightning strike against Denmark–Norway, shattering the regional balance of power. By exploiting Denmark’s encirclement of Swedish lands and the burden of the Sound Dues, Sweden transformed from a threatened neighbor into the undisputed master of the Baltic, setting the stage for a century of conflict.
The Torstenson War, lasting from 1643 to 1645, was a strategic masterstroke born from Swedish ambition. Despite Denmark–Norway having withdrawn from the broader Thirty Years' War in 1629, Sweden felt hemmed in by Danish territories that nearly encircled them. In the spring of 1643, the Swedish Privy Council decided that their military strength, honed by years of fighting in Germany under leaders like Gustavus Adolphus and Axel Oxenstierna, made territorial expansion at Denmark's expense both feasible and necessary.
The conflict began with a surprise multi-front offensive in May 1643. Field Marshal Lennart Torstensson marched from Moravia, seizing the Jutland peninsula by January 1644, while Gustav Horn occupied Danish provinces like Scania and Halland. Although King Christian IV of Denmark–Norway fought back with notable resilience, particularly at sea, his forces were exhausted. By the time the Peace of Brömsebro was signed on August 13, 1645, Denmark–Norway was forced to concede critical territories, including Jemtland, Herjedalen, and the strategic islands of Gotland and Øsel.
The treaty’s most significant blow was the exemption of Sweden from the Sound Dues, the tolls previously required for passing into the Baltic. This shift effectively ended the Danish-Norwegian dominium maris baltici and established Swedish hegemony. The war was not merely a territorial dispute; it was a fundamental realignment of power. Sweden gained unrestricted access to the North Sea and removed the threat of encirclement, while Denmark–Norway was left humiliated and desperate to recoup its losses. This cycle of aggression and resentment would fuel continued warfare across the Baltic for the next hundred years, as Sweden sought further expansion and its neighbors looked for any opportunity to reverse the new status quo.
Source: Torstenson War
