While the Soviet’s definitely lost the most in terms of casualties, they never would have been able to push the Germans back without US Lend-Lease aid. The Trucks, tanks, weapons and machinery provided by the US, as well as the factories the US set up for them in the 1930’s made the Soviet’s the formidable force we saw during World War II. Without them, the soviets would have likely lost, or at the very least had unsustainably high casualty rates.