The Molotov-Ribbentrop Pact and also the later Friendship Treaty put Finland and the Baltic states in the USSR's sphere of influence. Thus Germany lent no assistance to the Finns since there was no interest for them, and in fact was an active trading partner with the Soviets at that time.

Italy however had no such agreement with the Soviets, and allowed volunteers to go to Finland to fight Communism, and also shipped Carcano rifles to the Finns. The Allies also had great sympathy for the Finns, and volunteers poured in. An intervention was even planned, but the end of the war stopped that from happening, and once that happened, support for pissing of the Soviets diminished greatly.

However, after the Winter War ended, the Finns and the Germans began to buddy up. For the Finns, Germany was seen as a counter-weight to further Soviet pressure. For the Germans, once plans for invading the USSR were in the works in mid-1940, it was clear that Finland wanted her lost territory back, so would be willing to fight. A few months before Barbarossa was to be launched, the Finns were essentially told what was up, although not a detailed plan. They were soon brought on board, and launched the Continuation War in conjunction with the German invasion. Needless to say, Allied support for the Finns didn't exist this time, as the Soviets now were allies of convenience for the Western Allies.