The Winter War was a military conflict resulted from the invasion of Finland by the Soviet Union at the outbreak of World War 2.
Stalin, the dictator of the Soviet Union, probably thought to emulate the German blitzkrieg from the Invasion of Poland.
However, the purges he had made a few years earlier among the Red Army's officers, as well as the political commissars' control over the commanders, had resulted in a poor quality of the Soviet military leadership.
By the end of November 1939, the Red Army had concentrated at the border with Finland a numerically superior force in all aspects, especially the ratio in tanks and aircraft being vastly in its favor.
Most of the forces involved in the campaign on both sides concentrated in the Karelian Isthmus - a strip of land located between the Gulf of Finland and Lake Ladoga, crossed by the shortest way from Leningrad to the Finnish capital, Helsinki.
The Finns had built a series of fortifications in the Karelian Isthmus, surnamed the Mannerheim Line, which consisted of bunkers, trenches, anti-tank obstacles, and minefields.
The invasion of Finland by the Soviet Union began on 30 November 1939. After the first week, the course of the events seemed to confirm the Soviet optimism. The Finns retreated from the arctic port of Petsamo, as well as from the areas where they had planned actions of delay. On December 6, the Soviets reached the Mannerheim Line and next day captured the town of Suomussalmi in northern Finland.
However, the things went differently after the Red Army started the assaults on the Mannerheim Line. First at Taipale, then at Summa, the waves of Soviet infantry, sent again and again despite the heavy losses, fell one after another under the fire of the Finnish artillery, mortars, and machine guns. The lack of coordination with infantry led to the vulnerability of the Soviets tanks to the Finnish anti-tank teams.
Problems for the Soviets also arose from north of Lake Ladoga to the Arctic zone, where only a few roads crossed through a wilderness with many lakes and dense forests. The columns of the Soviet divisions were lengthening on dozens of miles due to the limited infrastructure and terrain. On the other hand, the Finns, moving fast and silently on skis, took the initiative launching sudden attacks. Tactics resembling more of guerrilla warfare led to spectacular victories against an enemy unprepared for them.
Stalin answered to the humiliations suffered during the first part of the Winter War, besides some usual executions, with the appointment of Semyon Timoshenko at the head of the Soviet Army in Finland. Timoshenko improved the coordination between the Red Army's branches, brought new infantry divisions and tank brigades, and focused only on the Mannerheim Line, abandoning the riskier forests from the north.
On February 1, 1940, thousands of Soviet guns launched the most powerful artillery barrage since the start of the campaign on the Finnish fortifications, which had been previously identified precisely by scouts. Timoshenko began a war of attrition that the Finns could not afford in the long run. From mid-February, the Finns retreated on successive lines of defense, compelled to cede land by losses in personal, increasingly difficult to replace, and the lack of artillery ammunition.
On 5 March, the Soviets entered Viipuri (Vyborg), which was the main city behind the Mannerheim Line. A few days later, the Finns accepted the terms imposed by Stalin, whereby the Soviet Union won little territory for an astonishing price of human lives and equipment.