German summer offensive towards Stalingrad, 7 May—23 July 1942 [Public domain, wiki]
The German army had taken Sevastopol, thereby eliminating any threat to its right flank, and was continuing its summer offensive deep into southern Russia. (Kharkov had already fallen in May.)
This week in the war, the Germans had broken through the Russian defenses around Kursk and, on 8 July 1942, were approaching Voronezh.
Panzer III and crew during the German offensive against Stalingrad, 1942 [Public domain, wiki]
Hitler’s intention was to eliminate the Russian armies in the bend of the River Don and then proceed eastward towards Stalingrad on the river Volga. By 10 July 1942, the German 4th Armoured Army had joined up with the 6th Army under General Friedrich Paulus
and was heading along the Don towards Stalingrad.
On 12 July, Stalin reacted to the German advance by appointing Marshal Semyon Timoshenko to command the Stalingrad sector.
If he could dispose of Stalingrad either by capturing the city or utterly destroying it by bombing, Hitler’s plan was to head south towards the Caucasus Mountains and to capture the oil-rich regions of Grozny and Baku.
In the end, the Russian defenses around Voronezh held—thereby eliminating the threat of Moscow being attacked from the south and subsequently encircled. But the Russians failed to hold Rostov. The fall of Rostov opened the way for the German army to advance south towards the Caucasus—exactly as Hitler had planned.