On this day, the Soviet Union cancelled its non-aggression treaty with Finland, in an escalation of the tensions between the two nations.
The non-aggression treaty was signed in 1932, and ensured that neither country attacked the other. The Soviet Union was determined to invade Finland in 1939, so it created a ‘false flag’ operation on its border with Finland. The Soviets shelled Mainlia, a town within Soviet territory, and then blamed Finland. This came to light years later, but at the time the ‘attack’ enabled the Soviets to claim Finland started the conflict.
At the time of the attack, Finland had offered to launch an investigation into the shelling of Mainlia, but the Soviet Union refused. Two days later, the Soviets would invade Finland.