Without US aid as well as the US fighting the Germans outside the European theater such as in North Africa, I think the Russians still ultimately end up defeating them but with even more devastation and loss of life than what they already endured. There is no doubt that having to fight a two front war was incredibly detrimental to the German war effort and it certainly sped up their defeat but without it the Germans still faced one major obstacle which is Russia as a country was so much larger than it population wise. France and Britain are similar sizes to Germany with similar populations and army sizes. So in a battle if France lost more mean than Germany then it was devastating.
Russia on the other hand was so massive a country that the Russians were able to move their factories and war production to the east far away from the Western Front and they had the people and resources to simply outproduce the Germans. To be sure what they were producing was of lower quality as were their soldiers in many respects but when you have the ability to produce say 10 tanks for every 1 German take or lose 10 men for every 1 German, eventually no matter how effective and efficient the Germans are, they are going to run out of resources and people.
There was on other thing that made this more likely as well. The Germans while enemies of the French and British treated them as humans. They considered them of similar stock to them hence why they occupied France. By contrast, Hitler considered Slavic people subhuman. So the Russians weren't merely fighting for their freedom like the French or British. They were fighting for their very existence because if they lost, their future wasn't simply an occupied Russia like an occupied France. Their future was gas chambers. This is an important point because there was no real avenue of surrender for the Russians which meant they would fight until the bitter end. So the Germans would literally have to conquer just about every part of Russia rather than simply defeat them in a few battles and then have them sue for peace like the French.
This is born out by the fact that the Germans actually wiped out much of the Red Army by 1941 ie the original 5 million man Red Army was almost entirely defeated. For a nation like France or Britain they would most likely have sued for peace similar to what Germany had to do at the end of WWI because doing so didn't mean extinction for them. Instead, Russia conscripted 8 million more men and continued the fight and there was another 8 million more behind that and so on and so forth. This was not a conventional war for Russia. This was only two outcomes. Victory or annihilation so every member of their population would have been thrust into the fight if needed.
The final factor IMO is the harsh Russian winter of 41/42. Assuming Hitler still attacks at the time he did, it doesn't matter how many people he threw at the Russians, the battle would still be halted by the harsh winter. I suppose you could argue he may have broken throw before the onset of winter but even if he had, he still would have to wait before proceeding deeper into the country which still would have given the Russian time to relocate their factories to the east. As I said in the other thread, the Germans essentially made it to like Phoenix or Las Vegas while the Russians had moved their factories to New York. That is a long way to go still against an enemy that has something like 10-15 times more people than you once you include the civilians/conscripts who were fighting for their lives.
I would say the best chance for Germany victory if we exclude US involvement would have been to finish the war with Britain first so that they could focus solely on the Western front and to attack Russia only after getting a firm commitment from Japan to attack from the East. The number 1 priority of the attack should have been to destroy the Trans-Siberian railroad as that is ultimately what won the war for the Russians was their logistical ability to move resources across such a massive country. Without it, their ability to wage war would have been crippled. With it, they always had the logistical advantage over the Germans and the Japanese because they had a well connected massive supply line all on land while Germany had to move supplies through various occupied countries and Japan via sea.
Yes and no.
It is true the Soviets moved most of their heavy factories east of the Urals and were able to restart production but most of the factories weren't able to come completely online until 1943. Part of the reason that Germany had such success in the summer of 1942 was because the Soviets simply didn't have the material available to effectively combat the Wehrmacht. Germany had complete air supremacy for most of 1942 and only began to see it slip at the end of the year. Even into 1943 the situation was close to a stalemate and only broke after the factories both came on line and the material supplied to the Soviets began to arrive in force.
The biggest assistance the US gave the Soviets was not in tanks or planes, although the Russians did welcome them (especially early in the conflict). The biggest assistance was the supply and logistical support that made the Red Army the force that it became. Thousands of US6 Studebaker trucks, among other models, were pretty much given to the Russians. The entire Red Army was supported by these vehicles and it is unlikely that the Soviet Army would have been able to maintain itself in the field. All of these trucks allowed Soviet industry the ability to concentrate on war production and avoid logistical support. There wasn't a need for truck factories because the trucks were being furnished by the US.
In addition much of the food producing regions of the Soviet Union were under German control until the end of 1943. Without US food shipments much of the population would have suffered and the Red Army would also have had to deal with food shortages. Even after much of the Ukraine and Western Russia were liberated the damage caused by the retreating Germans resulted in much of the land being unusable for months.
Personally, without Lend Lease the war would have dragged on another year at least, maybe two and it probably would have ended in stalemate. I suspect that in the end the Soviet Union would have survived the conflict but much of the western areas, including the Ukraine and the Baltic areas would have been taken by Germany. While the Soviets had a big supply of troops it wasn't endless. Estimates of Soviet losses in just KIAs during WW2 are estimated at between 7 and 9 millions. Injuries and prisoners add even more. Close to 4.5 million Soviets were captures. Wounded and missing was around 20 million. By the end of the war the Soviets were starting to have manpower issues but not at the level of the Germans.
Without the logistical help of the West the Soviets would have been much slower in the attack and would have taken much longer getting supplies and men into position. This would have allowed the Germans increased time to improve defenses and would have allowed much more freedom of movement for Wehrmacht forces.
This is my final opinion of the entire thing.
If the US didn't enter the war: The Soviet Union and England would have lost
If England didn't enter (or stay in) the war, the US and Soviet Union would have either lost or would have had to eventually make peace.
If the Soviets didn't enter the war, England and the US would have had to sue for peace.
I always hated the arguments over 'which was the most important Ally' because none of the participants would have been able to win if the others weren't involved. If the Soviets were fighting the Germans the mass of Nazi forces would have faced the US and British. There is little doubt that Hitler could have made France impregnable if he had at least half the troops he was forced to position in Russia. Without the US and Britain the Soviets would have starved or would have had to divert their own resources to supply and logistics and this would have made their chances of successfully driving the Germans all the way back to Germany less likely. The Brits and Russians would have starved if the US didn't get involved.
