Over the years I've had discussions with a few people about the Eastern Front in the Second World War. Some of those I've spoken with have asserted that Operation Barbarossa was always doomed to fail because of a combination of:
From reading Beevor's Stalingrad and from watching the Battlefield documentary on the same subject, I know that if the Nazis had won the famous battle it would have secured them access to the mineral wealth of the Caucasus and freed up forces to advance on Moscow and I believe that at one point the Nazis had occupied 90% of the city. Based on this fact it seems to me that rather than being doomed to failure the Nazis came perilously, frighteningly close to winning the war on the Eastern Front and if not occupying the entire USSR then at least removing it as a strategic threat for years to come.
I would therefore be very interested to read the opinions of any historians with a detailed knowledge of this period in history. To be clear, I very much hope that the Nazis were always doomed to fail in their conquest of the Soviet Union and that it wasn't simply sheer weight of numbers that won out for the USSR in the end.
Winning at Stalingrad would not have delivered the Caucasus to the Germans. If anything, it would have diluted the effort to seize the oilfields of Maikop and Grozny even more than it did in real life.
Stalingrad was emphatically not considered a priority target in German planning for 1942. The main target for Case Blue were the Caucasus oilfields. The plan envisioned securing the German left flank on the Don River, clearing the Don Bend, and then turning south into the Caucasus to seize the oilfields. Perhaps the only significance of Stalingrad to this particular plan was that it was a prominent crossing point on the Volga and thus potentially an area for the Soviets to mass for counterattacks. Field Marshal von Kleist is quoted as saying "it was just a name on a map to us".
It was only midway through Case Blue that Hitler insisted on capturing Stalingrad rather than just masking it. Army Group South was split into two new army groups, imaginatively called A and B. Army Group A under Field Marshal Fedor von Bock turned south towards the Caucasus and oil in Operation Edelweiss, while Army Group B under Field Marshal Wilhelm List drove for the Volga and Stalingrad in Operation Fischreiher. The original plan was to mask the Volga crossings, then turn south. Army Group South could not do both at the same time. Indeed, Army Group B's strength was so diluted that it had to leave huge stretches of the Don's south west bank unguarded, which later became the assembly areas for the Soviets' Operation Uranus after the Sixth Army had wasted itself trying to capture Stalingrad. That isn't to say that Case Blue in its original form could have succeeded: to advance from the Donets river to the Caucasus, Army Group South would have to travel distances greater than it had in Operation Barbarossa the previous year, over a much poorer road network, with understrength forces, against a prepared opponent, without the advantage of surprise, and in the middle of a fuel crisis.
I'm of the belief that it's not outside the bounds of realism to imagine a scenario where a more strategically-focused Germany might have forced the Soviets to seek armistice terms, for example, by Hitler enforcing unity of command in 1941 and insisting on seizing the Donbass rather than seeking to destroy the Red Army wherever it was found, or by seeking to close the Persian Corridor by bombing Astrakhan and Tbilisi, or by committing more forces to the Arctic theatre to cut the rail line to Murmansk. The Soviets took an incredible blow in 1941 that it's doubtful that any other nation could have come back from. However, with the mentality and the plan that the Germans invaded with, they were not going to achieve victory on the terms they had set with the army they had. They committed themselves to too many objectives over too much ground and in too little time, with nothing like the logistics to support it. And even if they had managed to get the Soviets to agree to terms, that doesn't mean it would have been anything like a sustainable peace.
Sources:
Antony Beevor, Stalingrad
Robert Kirchubel, Atlas of the Eastern Front, 1941-45