In September 1939, de facto allies Soviet Russia and National Socialist Germany conquered Poland and as part of the Molotov-Ribbentrop Pact, the Soviet Union then invaded Estonia, Lithuania, Latvia, and the Bessarabian region of Romania without fear of German interference. In late November 1939, Josef Stalin, the leader of the Soviet Union, set his sights on the next target: Finland.
On 26 November, the Soviets staged a false flag incident to justify the war. Four days later, 1,000,000 Soviet troops with 3,000 tanks poured across the border against 250,000 Finns and volunteers from other Scandinavian countries.
The Finns and their allies massacred the Soviet troops.
The Red Army was a ghost of its former revolutionary self in late 1939. In 1937 and 1938, Stalin’s purges killed off 90% of the Red Army’s officer corps. Only blind, dogmatic, and politically correct loyalty to Socialism and Stalin was the criteria for being a good officer. Furthermore, Stalin and his party apparatus murdered over 30 million people in those years. In this monstrous number included most non-Russian communists, including all Finnish communists who thought they were safe in their Russian exile. When the Soviets invaded Finland, former lieutenants were leading divisions, former sergeants: brigades and former privates: battalions, and no one was familiar with the terrain because any Finnish sympathizers were in mass graves.
The Finns and their allies were initially very successful. The Soviets were limited to attacking along unpaved roads on the mostly impassable Finnish frontier where they were endlessly ambushed by bands of Finnish ski troops. Or the Soviets had to frontally assault heavily fortified defensive belts on the Mannerheim Line, named after the Finns’ extremely competent and resourceful commander in chief, Field Marshal Gustaf Mannerheim. The Soviets suffered tens of thousands of casualties for no appreciable gain.
No amount of propaganda could cover up the grievous Soviet defeats. In January of 1940, Stalin had the Soviet commander killed. The new commander, General Seymon Timoshenko was one of the tiny number of senior commanders to survive the purges. He instituted the first of the Red Army’s much needed reforms. The reforms were basic and really only solidified and concentrated on the single Soviet tactic of the day, the frontal assault, but it was enough.
In late January 1940, the Finns were running out of ammunition and the Soviets were grinding through the Mannerheim Line. The British and French began supplying ammunition and supplies to the beleaguered Finns. Also, in one of the great “what if?” questions of the century, they planned on intervening directly with an expeditionary corps in March (though it was mostly meant to secure Swedish iron ore from the Germans). But it was too late. The Soviets broke through in late February and the Finns signed a peace treaty with the Soviet Union on 12 March.