What was the significance of hitlers offensive in the southern soviet union?

The offensive were a major turning point for the soviet red army

The German army made crucial gains, managing to push the red army as far as  25km to Moscow. Hitler however took command of the army and opted to take the southern oils fields of Soviet union and the town of Stalingrad. They were however trapped by winter, encircled by the red army and denied of food and supplies until their surrender.

Starvation, debt, financial downfall.