Answer
The Treaty of Roskilde, signed in 1658, marked a significant turning point in the Northern Wars. Denmark, under the rule of Frederick III, was forced to cede significant territories to Sweden, including the provinces of Scania, Halland, and Blekinge, as well as the island of Bornholm. This defeat profoundly impacted Denmark's geopolitical standing and ushered in a period of decline for the Danish monarchy.