Historically, defeating Germany required the three major powers. But can we do it with two?
1941: Moscow falls. To everyone's great surprise, the USSR continues to fight, but with the fall of its capital in 1941 the rest of the war is much bloodier. Although the Germans never reach Baku, they do reach the Caspian, and it's not til 1943 that they reoccupy Moscow.
D-Day still happens in the West, but with a stronger eastern front the war there takes longer. It's not until the bombings of August in 1945 that the Rhine is crossed.
What now?