Treaty of Nystad
By the Treaty of Brömsebro (1645), following the Torstenson War, Denmark-Norway ceded Jämtland, Härjedalen, Idre &amp; Särna, Gotland, Halland and Ösel to Sweden. Ösel and Dagö, islands off the coast of Estonia, were ceded to Russia in 1721 by the Treaty of Nystad. The other territories remained part of Sweden.