Karelian Isthmus in the context of "Mannerheim Line"

The Winter War was a war between the Soviet Union and Finland. It began with a Soviet invasion of Finland on 30 November 1939, three months after the outbreak of World War II, and ended three and a half months later with the Moscow Peace Treaty on 13 March 1940. Despite superior military strength, especially in tanks and aircraft, the Soviet Union suffered severe losses and initially made little headway. The League of Nations deemed the attack illegal and expelled the Soviet Union from its organization.

The Soviets made several demands, including that Finland cede substantial border territories in exchange for land elsewhere, claiming security reasons — primarily the protection of Leningrad, 32 km (20 mi) from the Finnish border. When Finland refused, the Soviets invaded. Most sources conclude that the Soviet Union had intended to conquer all of Finland, and cite the establishment of the puppet Finnish Communist government and the Molotov–Ribbentrop Pact's secret protocols as evidence of this, while other sources argue against the idea of a full Soviet conquest. Finland repelled Soviet attacks for more than two months and inflicted substantial losses on the invaders in temperatures as low as −43 °C (−45 °F). The battles focused mainly on Taipale along the Karelian Isthmus, on Kollaa in Ladoga Karelia and on Raate Road in Kainuu, but there were also battles in Lapland and North Karelia.

The Battle of Taipale was a series of battles fought during the Winter War between Finland and Soviet Union from 6 to 27 December 1939. The battles were part of a Soviet campaign to penetrate the Finnish Mannerheim Line in the Karelian Isthmus region to open a route into southern Finland. Despite their numerical superiority, the Soviet forces were unable to break through the Finnish defences.

Ladoga Karelia (Finnish: Laatokan Karjala, Swedish: Ladogakarelen, Russian: Ладожская Карелия, romanized: Ladožskaja Karelija, Карельское Приладожье, Karelskoje Priladožje or Северное Приладожье, Severnoje Priladožje) is a historical region of Karelia, currently largely in Russia. Today, the term refers to the part of the Republic of Karelia in the Russian Federation comprising the south-west part of the Republic, specifically Lakhdenpokhsky District, Pitkyarantsky District and Sortavala District. This region is on the northern littoral of Lake Ladoga, which borders Olonets Karelia to the East, Leningrad Oblast (Karelian Isthmus) to the south-west and the North Karelia region of Finland to the west.

Vyborg (/ˈviːbɔːrɡ, ˈviːbərk/; Russian: Выборг, IPA: [ˈvɨbərk]; Finnish: Viipuri, IPA: [ˈʋiːpuri]; Swedish: Viborg, IPA: [ˈvǐːbɔrj] ) is a town and the administrative center of Vyborgsky District in Leningrad Oblast, Russia. It lies on the Karelian Isthmus near the head of Vyborg Bay, 130 km (81 miles) northwest of St. Petersburg, 245 km (152 miles) east of the Finnish capital Helsinki, and 38 km (24 miles) south of Russia's border with Finland, where the Saimaa Canal enters the Gulf of Finland. The most recent census population of Vyborg is 72,530 (2021 census).

Vyborg was founded as a medieval fortress in Finland under Swedish rule during the Third Swedish Crusade. After numerous wars between the Russians and Swedes, the Treaty of Nöteborg in 1323 defined the border of eastern Finland, and would separate the two cultures. Vyborg remained under Swedish rule until it was captured by the Russians during the Great Northern War. Under Russian rule, Vyborg was the seat of Vyborg Governorate until it was incorporated into the newly established Grand Duchy of Finland, an autonomous part of the Russian Empire. Finland declared its independence from Russia in 1917, after which Vyborg became its second-most significant city after Helsinki, and represented internationally as its most multicultural city. During World War II, Vyborg's population was evacuated and the town was ceded to the Soviet Union. In 2010, Vyborg was conferred the status of "City of Military Glory" by Russian president Dmitry Medvedev.

Vsevolozhsky District (Russian: Все́воложский райо́н) is an administrative and municipal district (raion), one of the seventeen in Leningrad Oblast, Russia. It is located in the central northwestern part of the oblast on the Karelian Isthmus and borders with Priozersky District in the north, Kirovsky District in the south, Vyborgsky District in the northwest, Nevsky, Krasnogvardeysky, Kalininsky, Vyborgsky, and Kurortny Districts of the federal city of St. Petersburg in the west, and is washed by Lake Ladoga in the east. The area of the district is 3,036.4 square kilometers (1,172.4 sq mi). Its administrative center is the town of Vsevolozhsk. Population (excluding the administrative center): 153,045 (2010 census); 131,233 (2002 Census); 135,318 (1989 Soviet census).

Karelia (Finnish: Karjala: Swedish: Karelen) is a historical province of Finland, consisting of the modern-day Finnish regions of South Karelia and North Karelia plus the historical regions of Ladoga Karelia and the Karelian Isthmus, which are now in Russia. Historical Karelia also extends to the regions of Kymenlaakso (east of the River Kymi), North Savo (Kaavi, Rautavaara and Säyneinen) and South Savo (Mäntyharju).

Karelia may also refer to the region as a whole, including the portion of Karelia within Russia. The term "Finnish Karelia" refers specifically to the historical Finnish province, while East Karelia or "Russian Karelia" refers to the portion of Karelia within Russia. Finland ceded a portion of Finnish Karelia to the Soviet Union after the Winter War of 1939–40. More than 400,000 evacuees from the ceded territories re-settled in various parts of Finland. Finnish Karelians include the present-day inhabitants of South Karelia and North Karelia, as well as the still-surviving evacuees from the ceded territories.

Zelenogorsk (Russian: Зеленого́рск), known as Terijoki prior to 1948 (a name still used in Finnish and Swedish), is a municipal town in Kurortny District of the federal city of St. Petersburg, Russia, located in part of the Karelian Isthmus on the shore of the Gulf of Finland. Population: 14,958 (2010 census); 12,074 (2002 census); 13,032 (1989 Soviet census).

It has a station on the St. Petersburg-Vyborg railroad. It is located about 50 kilometers (31 mi) northwest of central Saint Petersburg.

Ingria is a historical region in what is now northwestern European Russia. It lies along the southeastern shore of the Gulf of Finland, bordered by Lake Ladoga on the Karelian Isthmus in the north and by the River Narva on the border with Estonia in the west. The earliest known modern inhabitants of the region were indigenous Finnic ethnic groups, primarily the Izhorians and Votians, who converted to Eastern Orthodoxy over several centuries during the late Middle Ages. They were later joined by the Ingrian Finns, descendants of 17th century Lutheran Finnish immigrants to the area. At that time, modern Finland proper and Ingria were both part of the Swedish Empire.

Ingria as a whole never formed a separate state; however, North Ingria was an independent state for just under two years in 1919–1920. The inhabitants of Ingria cannot be said to have comprised a distinct nation, since the population is made up of several different ethnic groups, despite the Soviet Union recognizing Ingrian as a nationality. The indigenous peoples of Ingria, like the Votians and Izhorians, are today close to extinction, together with their languages. This notwithstanding, many people still recognize and attempt to preserve their Ingrian heritage.