Moscow Peace Treaty in the context of "Interim Peace"

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 Finnish Democratic Republic (Finnish: Suomen kansanvaltainen tasavalta or Suomen kansantasavalta, Swedish: Demokratiska Republiken Finland, Russian: Финляндская Демократическая Республика), also known as the Terijoki Government (Finnish: Terijoen hallitus), was a short-lived puppet government of the Soviet Union in occupied Finnish territory from December 1939 to March 1940.

The Finnish Democratic Republic was established by Joseph Stalin upon the outbreak of the Winter War and headed by Otto Wille Kuusinen to govern Finland after Soviet conquest. The Finnish Democratic Republic was only recognised by the Soviet Union and nominally operated in Soviet-occupied areas of Finnish Karelia from the de facto capital of Terijoki. The Finnish Democratic Republic was portrayed by the Soviet Union as the official socialist government of Finland capable of restoring peace, but lost favor as the Soviets sought rapprochement with the Finnish Government. The Finnish Democratic Republic was dissolved and merged into the Karelo-Finnish SSR upon the signing of the Moscow Peace Treaty.

The Continuation War, also known as the Second Soviet–Finnish War, was a conflict fought by Finland and Nazi Germany against the Soviet Union during World War II. It began with a Finnish declaration of war on 25 June 1941 and ended on 19 September 1944 with the Moscow Armistice. The Soviet Union and Finland had previously fought the Winter War from 1939 to 1940, which ended with the Soviet failure to conquer Finland and the Moscow Peace Treaty. Numerous reasons have been proposed for the Finnish decision to invade, with regaining territory lost during the Winter War regarded as the most common. Other justifications for the conflict include Finnish President Risto Ryti's vision of a Greater Finland and Commander-in-Chief Carl Gustaf Emil Mannerheim's desire to annex East Karelia.

On 22 June 1941, the Axis invaded the Soviet Union. Three days later, the Soviet Union conducted an air raid on Finnish cities which prompted Finland to declare war and allow German troops in Finland to begin offensive warfare. By September 1941, Finland had regained its post–Winter War concessions to the Soviet Union in Karelia. The Finnish Army continued its offensive past the 1939 border during the invasion of East Karelia and halted it only around 30–32 km (19–20 mi) from the centre of Leningrad. It participated in besieging the city by cutting the northern supply routes and by digging in until 1944. In Lapland, joint German–Finnish forces failed to capture Murmansk or cut the Kirov (Murmansk) Railway. The Soviet Vyborg–Petrozavodsk offensive in June and August 1944 drove the Finns from most of the territories that they had gained during the war, but the Finnish Army halted the offensive in August 1944.

After the Munich Agreement, the Soviet Union pursued a rapprochement with Nazi Germany. On 23 August 1939, the Soviet Union signed a non-aggression pact with Germany which included a secret protocol that divided Eastern Europe into German and Soviet spheres of influence, anticipating potential "territorial and political rearrangements" of these countries. Germany invaded Poland on 1 September 1939, starting World War II. The Soviets invaded eastern Poland on 17 September. Following the Winter War with Finland, the Soviets were ceded territories by Finland. This was followed by annexations of the Baltic states and parts of Romania.

On 22 June 1941, Adolf Hitler launched Operation Barbarossa, an invasion of the Soviet Union with the largest invasion force in history, resulting in large battles and horrific atrocities. This offensive comprised three army groups. The city of Leningrad was besieged while other major cities fell to the Germans. Despite initial successes, the German offensive ground to a halt in the Battle of Moscow, and the Soviets launched a counteroffensive, pushing the Germans back. The failure of Operation Barbarossa reversed the fortunes of Germany, and Stalin was confident that the Allied war machine would eventually defeat Germany. The Soviet Union repulsed Axis attacks, such as in the Battle of Stalingrad and the Battle of Kursk, which marked a turning point in the war. The Western Allies provided support to the Soviets in the form of Lend-Lease as well as air and naval support. Stalin met with Winston Churchill and Franklin D. Roosevelt at the Tehran Conference and discussed a two-front war against Germany and the future of Europe after the war. The Soviets launched successful offensives to regain territorial losses and began a push to Berlin. The Germans unconditionally surrendered in May 1945 after Berlin fell.

During the early stages of World War II, the United Kingdom and France made a series of proposals to send troops to assist Finland against the Soviet Union during the Winter War, which started on 30 November 1939. The plans involved the transit of British and French troops and equipment through neutral Norway and Sweden. The initial plans were abandoned because Norway and Sweden declined transit through their land for fear that their countries would be drawn into the war. The Moscow Peace Treaty ended the Winter War in March 1940, which precluded the possibility of intervention.