The Americans and the British need Stalin. They know that supplies won't be enough, they need men power. The sacrifice of the russian troops by millions will able to destroy the nazi beast. In addition to american aid, Stalin wants to urgently open a second front meaning an ally landing in the West to divide german forces. Hitler is worry about a possible of an ally landing. He needs to finish of quickly in the East. He needs to put an end to Stalin and Stalingrad.
Stalin declares: "If we surrender Stalingrad, the south of the country would be cut of the center, we would lose our main water way and soon, our oil too". A quarter of century earlier, Stalin's rise to power began here, at Stalingrad, a city known at the time as Tsaritsyn. In 1918, Stalin had already a role in the first communist government.