On the Eastern Front , the Axis defeated Soviet attacks during summer and began its own main offensive to southern Russia along Don River and Volga River in June 1942 , trying to take over oil fields in Caucasus and a great steppe . On Germany 's eastern front , the Axis defeated Soviet offensives in the Kerch Peninsula and at Kharkov , and then launched their main summer offensive against southern Russia in June 1942 , to seize the oil fields of the Caucasus and occupy Kuban steppe , while maintaining positions on the northern and central areas of the front . The Germans split the Army Group South into two groups : Army Group A struck lower Don River while Army Group B struck south-east to the Caucasus , towards Volga River .