The Battle had been raging for months by November 19. Operation Uranus was the Red Army counteroffensive that launched pincers from the north and south that cut off Von Paulus' army from the main body of the German army.
By this date Von Paulus was already cut off but Hitler ordered him not to disengage and withdraw. Hitler said Von Paulus would be resupplied by air and relieved, none of which happened, of course.
Well they made a real effort to resupply Paulus but just couldn’t do it. Lost a lot of airplanes and pilots trying.
BTW, the general’s name is actually just Paulus rather than Von Paulus. I had a history professor tell the class that. I looked it up and sure enough he was right.
For some reason just about everyone puts the “Von” in there tho.