Finland–Russia border

The first treaty concerning the border was signed in Nöteborg in 1323 between Sweden (to which Finland belonged) and the Novgorod Republic. The Treaty of Teusina in 1595 moved the border eastward. As a result of the Ingrian War and the resulting Treaty of Stolbovo (1617), Sweden gained a large tract of land through the acquisition of the Nöteborg fortress, Kexholm and its large province, southwest Karelia and the province of Ingria. The Treaty of Nystad in 1721 and the Treaty of Åbo in 1743 moved the border westward.

Generally, the native populations on both sides of the border were ethnically Finnish. However, the border region was marked by religious differences, with the Russian side being predominantly Orthodox, while the Swedish side was initially Catholic, and later, Lutheran Protestant. After the peace of Stolbovo in 1617, the Orthodox population faced persecution and many fled to the Russian side or converted to Lutheranism. The displaced population was largely replaced by immigrants from Finland, most of whom were Savonians who spoke Finnish instead of the closely related Karelian.

After the Finnish War, the Treaty of Fredrikshamn transferred Finland from Sweden to the Russian Empire, with the territory becoming a Russian possession known as the Grand Duchy of Finland. In 1812, the Finnish–Russian border reverted to its pre-1721 location, granting the Grand Duchy so-called "Old Finland" territories previously held by Sweden.

Treaty of Tartu in 1920: Repola and Porajärvi, occupied by the Finnish government, were returned to the Soviet Union, while Petsamo was gained by Finland.

In the period following Finland's 1917 independence declaration, during the Finnish Civil War and Russian Civil War, Finnish activists often crossed the border into Soviet territory in order to fight in the "heimosodat" wars surrounding Finnish ethnic self-determination and possible annexation into Finland. This ended in 1920 when the Russian–Finnish Treaty of Tartu in 1920 defined Finland as an independent country and established the border between the two countries. Despite this, Finnish fighters took part in the East Karelian uprising and Soviet–Finnish conflict of 1921–22. In 1922, the Finnish government closed the border to volunteers and food and munitions shipments.

Territorial losses of Finland to Soviet Union in conclusion to World War II; Porkkala was returned in 1956.

In 1939, the Soviet Union invaded Finland in the Winter War, leading to the signing of the Moscow Peace Treaty the following year. The treaty had Finland cede several border areas to the USSR.

The naval border was established in 1940 and more accurately defined in 1965.

Between 1940 and 1941, the Soviet Union rented Hanko Peninsula as a military base, thereby creating an additional border crossing leading to the exclave.

After the Continuation War (1941–44), the land border was demarcated in the Treaty of Paris (1947). As a result, approximately half of Finnish Karelia (including Finland's fourth-largest city Vyborg), parts of Salla, and all of Petsamo were ceded to the Soviet Union. The new border cut through what was previously Finnish territory, severing many rail lines and isolating many Karelian towns from Finland. The Soviet Union demanded the territories be emptied, and Finns were subsequently evacuated from the area and resettled in Finland. The areas that they left were then settled by Soviet immigrants.

In the Moscow Armistice signed in 1944 between Finland, the Soviet Union and the United Kingdom, a small peninsula towards the Gulf of Finland, Porkkala, was rented to the Soviet Union as a military base. This created in effect a southern border crossing to the Soviet exclave. Border crossings were in Luoma (checkpoint) and Tähtelä. In 1947, Finnish trains were allowed to pass through the base, but the passenger car windows were blinded and the locomotives replaced while crossing through. Porkkala was returned to the Finnish government in 1956.

Border zone in 1967

During the Cold War, the border constituted part of the perimeter of the Iron Curtain. Crossing the border was not possible for much of its length. Only a very limited number of border crossing points existed, and the Soviet government permitted only escorted trips to select cities; border zones were off limits to tourists.[7] There was little contact between cities that were relatively close to each other on opposite sides of the border, such as Imatra and Svetogorsk.

The Soviet side maintained extensive electronic systems and patrols to prevent illegal crossings. Soviet border surveillance began at a great distance from the actual border, and was as extensive as elsewhere along the Iron Curtain. The first surveillance systems were installed in railway stations in cities, where the militsiya monitored potentially suspicious traffic. The border zone began at 120 kilometres (75 mi) from the border. A special permit was required for entry, and the first line of control was equipped with electronic alarms. At 60 kilometres (37 mi), there was a raked sand strip (to detect footprints) and a thin alarmed tripwire. At 20 kilometres (12 mi), there was a 3 metres (9.8 ft) tall barbed wire fence, with a top that curved inwards towards their own territory to prevent Soviet citizens from leaving. The fence had an electronic alarm system. However, it was not protected underground and tunnelling under it was possible. On the Finnish side, there was a border zone where entry was allowed only with a permit, and a "reindeer fence" closer to the border. Finally, at the international border, there was a border vista. Since Finland was a neutral country for most of the Cold War, they did not protect illegal border crossers and instead returned them to the Soviet authorities if captured. As a result, illegal border crossers had to arrive in a third country, for example Sweden, in order to defect to the West.[7]

Both states verified the inviolability of borders and territorial integrity in the first Conference on Security and Co-operation in Europe in 1975.