Russo-Swedish War (1741–1743)
The Hats' Russian War (1741-1743) was the Swedish participation in the War of the Austrian Succession (1740-1748). It was concluded by the Treaty of Åbo where Sweden ceded the areas of southern Karelia around the Kymi river and Savonlinna to Russia. This territory and the territories lost in the Treaty of Nystad which ended the Great Northern War in 1721 were later referred to as Old Finland.