4. Soviet Union
The Soviet Union was a great military power heading into World War 2. It had the largest standing army at that point, equipped with sizable inventories of weapons, including the biggest fleet of battle tanks in the world estimated at 30,000 in number. In the years preceding the conflict, Stalin had also established several self-sufficient heavy industries at home capable of producing tanks and ammunition on a large scale. It also sought rapprochement with Nazi Germany and signed a non-aggression pact with Hitler’s government a week before the start of the conflict. However, after the collapse of France, in 1941, Germany launched Operation Barbarossa against the Soviet Union, which was one of the largest invasions in history. Around 27 million Soviets lost their lives during the war.