Operation Weserübung's effects on Sweden became strategically encircled by the German-Soviet pact. Since the Baltic states; Estonia, Latvia, and Lithuania; had been forced to accept "limited" Soviet forces on their soil, in the autumn of 1939, they were de facto more or less in a state of occupation. For Sweden and Finland, this meant that the only possible trade route to nations other than Germany and the Soviet Union, was through Petsamo harbour, in the far north of Finland. This seriously hampered the supply situation in both these nations. It also meant that an invasion of Sweden could be launched from almost any direction. Sweden
Finland–Sweden border in a topographical description made in 1811. The border was decided to run through the geographical centre of the island (defined by coordinates) in the treaty of Åland in 1921 and in the treaty of continental plates in 1972. The Märket lighthouse, built in 1885 by Finland and operated by them, was left on the Swedish side. In 1981, the border on the island was modified into a curve to get the lighthouse on the Finnish side. The border is agreed to be regularly inspected every 25 years. During the independence of Finland, inspections have been made in 1926–1927, 1956–1957,