Treaty of Fredrikshamn in the context of "Finnish War"

Finland was an integral part of Sweden from the Middle Ages until 1809. The starting point of Swedish rule is uncertain and controversial. It is traditionally linked to the First Swedish Crusade in the mid-12th century. Historical evidence of the establishment of Swedish rule in Finland exists from the middle of the 13th century onwards.

Swedish rule ended in 1721 in most of so-called Old Finland, the south-eastern part of the Finnish territories, as a result of the Great Northern War. Sweden ceded the remainder of Old Finland in 1743, following the Hats' War. Swedish rule over the rest of Finland ended on 17 September 1809, when the signing of the Treaty of Hamina ended the Finnish War. As a result, the eastern third of Sweden was ceded to the Russian Empire and became established as the autonomous Grand Duchy of Finland.

Ostrobothnia (Swedish: Österbotten; Finnish: Pohjanmaa) is a historical province comprising a large portion of western and northern Finland. Before the Treaty of Fredrikshamn in 1809, Ostrobothnia was part of Sweden. It is bounded by Karelia, Savo, Tavastia (Häme) and Satakunta in the south, the Bothnian Sea, Bothnian Bay and Swedish Norrbotten in the west, Lapland in the north and Russia in the east.

Märket ('The Mark', Swedish pronunciation: [ˈmæ̂rːkɛt]) is a 3.3-hectare (8.2-acre) uninhabited skerry in the Baltic Sea shared by Sweden and Finland (in the area of the autonomous region Åland), with a lighthouse as its salient humanmade feature. Märket has been divided between the two countries since the Treaty of Fredrikshamn of 1809 defined the border between Sweden and Grand Duchy of Finland as going through the middle of the island. The Finnish side of the island is part of the Municipality of Hammarland in the autonomous region of Åland and is the westernmost land point of Finland. The Swedish part of the island is itself divided between two counties of Sweden: Uppsala County (Östhammar Municipality) and Stockholm County (Norrtälje Municipality).

Finland Proper or Southwest Finland (Finnish: Varsinais-Suomi; Swedish: Egentliga Finland) is a historical province in southwestern Finland, administered by its historic capital of Turku (Swedish: Åbo). Before the Treaty of Fredrikshamn in 1809, it was part of Sweden. It borders Satakunta, Tavastia (Häme), and Uusimaa. It is also bounded by the Baltic Sea facing Åland. The historical provinces have no administrative function today but live on as a historical legacy in Finland and Sweden.

The modern region of Southwest Finland largely corresponds to the historical province. However, the modern region includes Loimaa, which was historically part of Satakunta, and Somero, which historically belonged to Tavastia.