Britain drops out of the war in 1940 and the Reich never declares war on the US.
Germany can now devote most of their resources, vehicles, manpower, and effort against the USSR in time for Operation Barbarossa. The USSR is still getting Lend Lease though.
Can Germany not distracted by other fronts and campaigns (air, naval, Africa etc) defeat the USSR?
How much does not fighting the US/UK increase the Reich's chances of victory against the USSR?