I once created a "take-off" on Civilization II to answer questions like that. While I have only a "beta" copy of my version, I could get some very interesting results using a "whole world" board for World War II (not just Europe as in the Civ II version). I'll supplement the results by using "real world" battles.
The seven countries are America, Britain, Soviet Union, Germany, Japan, "Neutrals" (e.g. Spain and Turkey in a grand coalition), and "China" (four cities in the back country, Yenan, Chongqing, Llass, and Urumqi).
My theory is that in order to win on the Soviet front, Germany needed to capture both Kiev and Moscow in 1941. And they couldn't. It was one or the other, and they opted for Kiev first, which is why the couldn't get Moscow, and ultimately why they couldn't win the war.
If they advance on Moscow in the fall of 1941, they forego their attack on Kiev. They capture part of the city by December, but by then it's winter, and they barely hold their positions, more or less, as in real life. It takes them until summer to capture the city entirely, and by the time they have finished mopping up partisans (an important feature of the Civ II game), it's almost fall. By the end of 1942, the Germans have captured Moscow and possibly Leningrad, but have let the "big prizes," the southern economic zones, stay Russian.
Meanwhile, the Americans have destroyed the Japanese navy in the battle of Midway, in June, 1942, and the Anglo-Americans have captured North Africa by early 1943. When the Germans resume advancing on southern Russia in summer 1943, the Russians are backed up by Anglo-American troops coming through Persia and the Caucasus. Other American and British forces open a "second front to the north and east; the British land in Archangel (after winning the battle of the Atlantic in the spring, 1943), and the Americans land in Siberia, joining up with the "locals," and attacking German holdings in Russia from the east. All, like the "White Russians" against the Communists in 1919-20 (the British actually occupied Archangelsk at the time. Joint Anglo-American-Russian forces beat the Germans west of the Urals, invade East Europe together (the Anglo-Americans invade Italy in 1944 to co-ordinate around the Black Sea.
The key is that the Americans get involved with Lend Lease, and a modicum of ground troops. In that way, "locals" will rally around them.