Final answer:
The Soviet Union under Stalin played a crucial role in WWII, enduring massive initial losses due to the German invasion, but eventually repelling the Nazis through scorched-earth tactics and the relocation of industrial capacity, leading to over 25 million Soviet casualties.
Step-by-step explanation:
The Soviet Union's participation in WWII under Stalin's command is best described by the events that unfolded after the betrayal of the non-aggression treaty with Nazi Germany, known as Operation Barbarossa. The purges of the 1930s had already weakened the Soviet defense by removing experienced commanders from the military. Despite being initially unprepared and suffering devastating losses, Stalin's actions such as the relocation of factories and implementation of scorched-earth tactics allowed the Soviet Union to withstand and eventually repel the German invasion. In doing so, Stalin and the Soviet people endured a huge human cost, with more than 25 million Soviets dying on the eastern front during the war.
Leaders like General Georgy Zhukov were instrumental in turning the tide of the war, evidenced by the success of the Soviet pincer move at Stalingrad, which ultimately led to the surrender of the German 6th Army. The Soviet Union, despite being subjected to initial onslaughts, played a significant role in the eventual defeat of the Nazi regime, shaping the outcome of World War II.