The winter war (talvisota, зимняя война) was a military engagement between finland and the ussr lasting three months, from november 1939 to march 1940, three months in which the ussr, even though the victor of the war, suffered heavy losses beacause of poor tactics in face of a much better organised army, and beacause of the lack of officers, all having been shot in the purge which was basically still going on.
The finnish fought heroically in face of an enemy who outmanned them at one hundred to one, and outmaneuvered the soviets, who in the end overcame the finnish defense ( lots of over’s, yea). The winter war is a good example of guerilla warfare as well.
The cause of the war was a refused soviet territory requirement claiming security reasons, and ended in the ussr’s expellment from the league of nations, the latter having decided it was an illegal attack.
The winter war continued itself in the Continuation war of 1941 (original name, ik, wikipedia it).
1. A man stands beside a broken soviet KV-1 tank (possibly a finn judging by the attire).
2. Even though rare, since the finnish had great respect for the dead and often allowed retrieval of them, there are a few documented cases of dead being used in psychological warfare.