Winter War. Covers the 1939-1940 war between Finland and the Soviet Union. The Soviets have a massive strength advantage but their heaviest units can't be used north of the arctic circle and all Soviet units must be able to trace a supply line back to Leningrad at all times. Finnish units don't need supply in Finland, they have the advantage of prepared defenses south of the arctic circle, and Finnish units have higher mobility than Soviet units.