The Treaty of Fredrikshamn on September 17, 1809, concluded the Finnish War between Russia and Sweden. The treaty was signed in the present-day Finnish town of Hamina.
According to the treaty Sweden ceded Åland, parts of the provinces Lapponia and Westrobothnia (east of the rivers of Tornio and Muonio) and all provinces east thereof.
The ceded terrotories came to constitute a Russian Grand Duchy, to which also the 18th century conquests of Karelia including parts of Nyland and Savonia were later annexed (see: "Old Finland").
Together with the Porvoo Diet (1809) the Treaty of Fredrikshamn constitutes the cornerstone for the autonomous Grand Duchy of Finland, and thereby the start of the development which would lead to the revival of Finnish language and culture, and ultimately in 1917 to Finland's independence.
Also for Sweden, the treaty turned out to be ultimately beneficial. During the negotiations, Swedish representatives had endeavoured to escape the loss of the Åland islands, "the fore-posts of Stockholm," as Napoleon rightly described them. (The Åland islands were additionally culturally, ethnically and linguistically purely Swedish, but that was of no significance at that time.) In the course of the 19th century it would also turn out that the Åland islands were a British interest, which after the Crimean War led to the de-militarization of the islands according to the Åland Convention included in the Treaty of Paris (1856). Instead of the Åland islands, Sweden came to retain vast areas in the far North, already conquered by the Russians, where later important iron ore and hydropower were to constitute the basis for Sweden's rapid 20th century industrialization.