It was the Russians though that destroyed the German army. The army that the Americans and Brits faced in France and Germany was a mere shadow of what would have faced them if the Russians hadn't done the vast majority of the killing.
Oh, and the German advance was stopped before December '41
Siege of Leningrad Begins Sept 9 1941 – Three months before the entry of US into WWII. Germans never take Leningrad. Germans checked on Northern Front. Siege lasts until 1944.
Siege of Moscow Begins 30 September 1941 – Two and a half months before the entry of US into WWII. Germans held on Central Front. Russian counter-offensive begins on 5 December 1941. 1 Day before attack on Pearl Harbour.