The German forces attacked the Soviet Union towards the south to the city of Stalingrad. The battle was a turning point of the war. The Soviet army encircled the German army troops when they reached the city and counterattacked the forces.
After a month of fierce fighting and a lot of casualties, the remaining surviving German force surrendered and decided to retreat back. They began the long retreat towards the west.
I'm not 100% sure but it could be: Voluntary Exchange takes place between buyers and sellers: (btw I copied and pasted from the question so I didn't take any content :D)
