This is because the Allies had different roles which are attacking on different fronts and colonies. America, Canada, and Great Britain fought in the Western Front in which they started to attack German liberated Europe in Normandy on June 6, 1944. Germany betraying and invading Russia was the moment Hitler started to lose the war (Operation Barbarossa). Russia was able to defeat Nazi Germany mainly because of the cold winter and Stalin moving their factories East to make a ton of supplies to fight back against the Germans. The Battle of Stalingrad known to be the bloodiest battle of ww2 and one of the deadliest in history, was when the USSR started to do good progress to pushing the Nazis back a lot. The Battle of the Bulge in the western front is when the German army started to get a lot more weaker since Hitler wanted to encircle Belgium which failed and made a nice bulge. The Allies were able to regain that bulge.
