The western front was more or less a sideshow. All of the big battles were in the East. The Soviets kept bottled up a German force fully half as big as were fielded on the whole western front, in a little peninsula of Latvia ("Courland Pocket"), for almost a year.

But the naval war in the Atlantic mattered. And, US supplies (particularly SPAM, and trucks, tires, and fuel) delivered through Iran were helpful late in the war.

But aside from naval work that denied Germany South American resources, the Soviets could have done the whole job on their own, and would have overrun all of Europe. In particular, there is no evidence that British and US area bombing achieved anything, although point attacks on rail locomotives did.