Historians have had a great deal of difficulty accounting for the debacle wrought by Operation Barbarossa. How could the Red Army, a large and heavily equipped force, be so thoroughly decimated by the Wehrmacht, especially when evidence of the impending attack was plentiful? Most commonly, explanations have focused on the unexpectedly rapid success of the Blitzkrieg in western Europe, the impact of the Great Purges on the Soviet officer corps, the problems of reequipping the Red Army with modern weaponry and protecting newly expanded borders, the lack of adequate training for the rapidly growing Soviet armed forces, the confusing nature of available intelligence, and, most of all, the nearly fatal self-delusion of Iosif Stalin, which prevented the implementation of proper defensive measures. Although Stalin certainly realized that the Nazi-Soviet Pact was no more than a temporary truce and that a German attack was ultimately inevitable, he deluded himself that Adolf Hitler could be appeased until Soviet forces had grown strong enough to meet the Nazi assault. Soviet shipments of petroleum products, various raw materials, and foodstuffs were critically important to the German war machine and, thus, the key element in Stalin's strategy of appeasing Hitler.