By sheer scale, attrition, and strategic impact, this is clearly the biggest deciding factor on the war (But not fully as Japan wasn't involved) It absorbed and destroyed roughly 75% to 80% of all German Wehrmacht casualties, effectively breaking the back of the Axis war machine. But sheer scale and casualties is not always easy to calculate. Obviously most deciding campaign is Operation Barbarossa and it's failure to bring quick victory and start industrial scale of war of attrition. But what do you guys think? Eastern front perhaps deserves it's own topic too