Finland–Russia border

The first border treaty concerning this 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. In conclusion to the Ingrian War, Sweden gained a large tract of land through the acquisition of the Nöteborg fortress, the Kexholm and its large province, southwest Karelia and the province of Ingria in the Treaty of Stolbovo (1617). The Treaty of Nystad in 1721 and the Treaty of Åbo in 1743 moved the border westward.

The main difference between the different sides of the border at the time was religion. The Russian side was Russian Orthodox, the Swedish side was Catholic, later Lutheran Protestant. Generally the native population was ethnically Finnish and Finnish-speaking immediately on both sides of the border. However, after the peace of Stolbovo in 1617, the Orthodox population was persecuted and either fled to Tver or converted to Lutheranism and started speaking Finnish instead of the closely related Karelian. The population was largely replaced by immigrants from Finland, most of which were Savonians.

After the Finnish War, the Treaty of Fredrikshamn converted all of Finland from Swedish territory to a Russian possession, the Grand Duchy of Finland. The Finnish–Russian border was moved back to the pre-1721 location, so that the Grand Duchy gained the so-called "Old Finland", territories previously held by Sweden, in 1812.

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.

After Finland became independent in 1917, there was the Finnish Civil War in 1918, and even after this war, the Russian Civil War continued. Finnish activists often crossed the border into Soviet territory in order to fight in the "heimosodat", wars aiming at Finnish ethnic self-determination and possible annexation into Finland. However, this came to an end in 1920, when the Russian/Finnish Treaty of Tartu in 1920 defined Finland as independent and demarcated the countries' common border. However, Finnish fighters would still take part in the East Karelian uprising and Soviet–Finnish conflict of 1921–22. Finally, the Finnish government closed the border from the volunteers and food and munitions shipments in 1922.

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

During World War II, Stalin severely suppressed the native Finnish-speaking population (Ingrian Finns) by population transfers, collectivization and purges, such that border zones were to be free of Finnish peoples.

The land border was later demarcated in the Treaty of Paris (1947) following the Continuation War (1941–44), in which Finnish Karelia, including Finland's second-largest city Vyborg, parts of Salla and Petsamo were ceded to the Soviet Union. The new border cut through Finnish territory proper, severing many rail lines and isolating many Karelian towns from Finland. The Soviet Union demanded emptying the territories first. Finns were evacuated from the area and resettled elsewhere in Finland; almost nobody was willing to stay. The areas were resettled by Soviet immigrants. The Porkkala naval base was leased by the Soviet Union, but returned to the Finnish government in 1956. The naval border was established in 1940 and more accurately defined in 1965.

The border is uncontroversial and clearly defined by law.[8] Both states verified the inviolability of borders and territorial integrity in the first Conference on Security and Co-operation in Europe in 1975.

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.[9] There was little contact between cities that were relatively close to each other on opposite sides of the border, such as Imatra and Svetogorsk. On the Finnish side, there was a border zone where entry was allowed only with a permit, but habitation was permitted and residents could continue living in the area. The Soviet side had extensive electronic systems and patrols to prevent escapes. 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 was already 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 had 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 Soviet territory. The fence had an electronic alarm system. However, it was not protected underground and tunnelling under it was possible. Finally, at the international border, there was a border vista. In the north, this was followed by a Finnish reindeer fence. Unlike other Western countries, the government of Finland did not protect illegal border crossers but returned them to the Soviet authorities if captured. Illegal border crossers had to get through Finland to e.g. Sweden in order to defect to the West.[9]

In the Moscow Armistice signed on 1944 between Finland, Soviet Union and United Kingdom, a small peninsula towards the Gulf of Finland, Porkkala, was rented to Soviet Union as a military base. This created in effect a southern border crossing to the Soviet exclave, operating all the way to 1956. 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 locomotive replaced while crossing through. Earlier between 1940–41, Soviet Union had rented Hanko Peninsula as a military base. Apparently there was also a border crossing to the exclave at the time.