The Torstenson War (1643–1645) was a conflict between Sweden and Denmark-Norway that arose during Sweden’s expansionist efforts following its success in the Thirty Years' War. Named after Swedish Field Marshal Lennart Torstenson, the war marked Sweden’s bid to weaken Denmark-Norway's dominance in the Baltic Sea region, driven by geopolitical competition and longstanding grievances, such as Sweden's irritation over the Sound Dues, the toll Denmark-Norway imposed on ships passing through the Øresund Strait.
Sweden's military success in the Thirty Years' War emboldened the Swedish leadership to address the territorial and economic advantages Denmark-Norway held due to its control over key regions surrounding Sweden. By 1643, the Swedish Privy Council decided to launch a multi-front surprise attack on Denmark-Norway. Swedish forces under Torstenson invaded Jutland in December 1643, quickly capturing it. Simultaneously, General Gustav Horn led an invasion of Scania and Halland, gaining substantial ground. Despite Denmark-Norway's initial shock, King Christian IV managed to protect the Danish heartland with his navy, though he suffered defeats like the Battle of Fehmarn in October 1644.
On the Norwegian front, Governor-General Hannibal Sehested led a reluctant Norwegian force into Sweden, while Swedish troops temporarily captured Jämtland and advanced into Norwegian territory. Despite some tactical successes by Norwegian troops, overall Danish-Norwegian efforts could not turn the tide of the war.
The war ended with the Second Treaty of Brömsebro in 1645, which forced Denmark-Norway into significant territorial concessions. Sweden gained the Norwegian provinces of Jämtland, Härjedalen, Idre, and Särna, as well as the Danish islands of Gotland and Ösel. Sweden also secured a 30-year occupation of Halland and was exempted from paying the Sound Dues, thereby effectively breaking Denmark-Norway's monopoly over Baltic trade routes.
The Torstenson War was a pivotal moment in Swedish history, significantly bolstering Sweden's territorial power and marking the end of Denmark-Norway's control of the Baltic Sea. These gains set the stage for Sweden's Age of Greatness and further conflicts with Denmark in subsequent wars, as Sweden continued to assert dominance in the region.