Stalingrad
The failure to capture Moscow before the beginning of winter was a setback for Hitler, but it would not have made much difference to the war. Even if Moscow had fallen, the Russians would have continued to fight - just as they had done in 1812 when Napoleon's army occupied the city.
In 1942 Hitler decided to concentrate his attack on the Caucasus oil fields. This would mean occupying Stalingrad as well. However, in trying to seize both Stalingrad and the oil fields, the Germans risked gaining neither. Army Group South would have to be split in two and so would be weakened. The battle for Stalingrad was fought from September 1942 to January 1943. The Russians fought ferociously to hold on to the city. It became a symbol of their defiance. It also became an obsession for Hitler and he recklessly threw away an army of 330,000 men in an effort to take it. On 31 January the German commander, von Paulus, disobeyed Hitler's order to fight to the death and surrendered what was left of his original army: just 91,000 troops.
Stalingrad was a turning point of the war in the East. The Caucasus oil fields escaped capture and the Germans were now desperately short of fuel. It was the Russians' first real victory of the war and it proved to them that the Germans could be defeated. The morale of the Russian troops - essential for any army - was dramatically boosted. From now on, the Germans were steadily driven back.
Neil Demarco: The era of the Second World War; Oxford University Press, 1993/2000, page 40