Answer: The Battle of Stalingrad
Details:
Germany had invaded the Soviet Union in what they called Operation Barbarossa, beginning in June, 1941. The Battle of Stalingrad, fought from August 1942 to February 1943, became the turning point in the war between German and Soviet forces on the Eastern front of World War II. Stalingrad was a protracted and extremely bloody military confrontation. More than 2 million troops were involves, and the death toll (including many thousands of Russian civilians) also numbered around two million. As reported by the History Channel, "The Battle of Stalingrad (one of Russia’s important industrial cities) ultimately turned the tide of World War II in favor of the Allied forces."
A India India has the highest population and population density
