The Battle of Stalingrad was the most important battle of WWII.

Men are much easier to replace than tanks (German tanks at least) because they can just be trained more. Training for the average German infantryman consisted of six weeks at boot camp and then being given a rifle and being put on a train bound for the front. A tank took on average about four months to build and then send to the frontline after tests.The value of the equipment of an average modern US soldier is roughly $50,000. That includes the items that would not be given to a German soldier at that time, such as flakjacket, a particularly sophisticated helmet, the weapons used by a US soldier and the communications equipment. It is estimated that the value of a German soldier's equipment equates to roughly $10,000 in today's money. This is one seventy-fifth of the value of a Panther Tank, and about a twenty-fifth of the value of the average medium gun. As Cicero said, 'the sinews of war are infinite money', and WWII was no exception. If we take money as meaning all resources that had intrinsic values such as steel, petrol, food and cement, this was Germany's undoing. The bombings had a huge impact on German industrial capacity, rendering it a hopeless economy. It is a fallacy to say that this had no effect on the outcome of the war.The Wehrmacht had about eighteen million total personnel, the Regio Esercito about seven million, and the Balkan states and Vichy France about two million. That brings the Axis' total strength to roughly 27,000,000 personnel. Obviously, this did not mean 27,000,000 soldiers at the front line. It meant 27,000,000 soldiers, labourers, field engineers, medical staff, communications staff, general staff and others, which resulted in approximately 15,000,000 soldiers on active duty.The USSR had about 25,000,000 personnel, roughly 16,000,000 of which were active servicemen. Record keeping was not one of the Red Army's fortes, and this figure takes account of any number of men that were present at the front, but were unregistered as part of the armed forces. I have also taken account of Soviet deserters to the Axis, as well as the various anti-communist militia groups that they had picked up during the invasion, which largely consisted of the former White Army cossacks that Stalin had not managed to tame through starvation. There was very little of this among the Allies, since their record keeping was probably the best of any side during the war, though admittedly it is probably due to the large numbers of destroyed or misplaced German and Soviet documents that occured during the war.The Allies, by which I mean Britain, the Commonwealth and the USA (the figures would be distorted if I included Chinese and Native African forces present in the war, which had a negligable impact on the war in Europe), had roughly 20,000,000 personnel, of which approximately 12,000,000 were active servicemen posted to the various fronts.So let's deal with the revised strengths.Axis (excluding Japan) total personnel - ~27,000,000USSR total personnel - ~25,000,000Allies total personnel - ~20,000,000Axis (excluding Japan) total active personnel - ~15,000,000USSR total active personnel - ~16,000,000Allies total active personnel - ~12,000,000With a total armed forces that was the largest in Europe, the Axis powers were certaily in with a chance on paper. The only thing the figures disguise is the materiel the sides had. For the tactics and strategies employed by the Axis to work, they required huge numbers of tanks, planes, trucks and artillery guns. This sucked up Germany's economic power to produce, and the tanks and guns destroyed at Kursk were irreplacable due to the high value of the materials and expertise required in producing them. Germany had effectively thrown away its most expensive army, and enabled the Soviets to push them back along that front to the Dnieper and beyond.From then on, the war was a large-scale version of the Abyssinian War, with Germany taking the role of Ethiopia and the USSR taking the role of Italy.Two million soldiers would have been a serious dent in the Soviet lines, and though it would be replenished in time, it would have given the Germans the opportunity they needed to capture the ruins of Stalingrad and the Caucasus Oilfields for certain, and may have prevented the USSR from relieving Leningrad. The shock would have paralysed the Ukrainian and Caucasus fronts for weeks, even months, and Germany would have had a repeat of June-October 1941, fighting against a disorganised mass of infantry and scattered armour.After Stalingrad, the German Army was still largely intact. It had suffered a shock on its localised power and morale, but it was still capable of recovering.After Kursk however, the German Army was a mass of infantry in full retreat. Operation Citadel was the last offensive operation mounted by the Axis for the remainder of the war. The rest of the war was one long, bloody retreat back to Berlin.