Let’s see some facts:
1. Hitler had the perfect army but the worst mind – from the Treaty of Versailles the could not have a big army, but for that they had better equipment
2. USSR did not participate in the war until the invasion of USSR so until that time the only real fighting ally was Britain
3. USSR lost 27 million people and that was the highest toll in the whole was + USSR took the most territory of the territory under the Axis control
4. USA greatest victories in the war was D-Day and Japan, but Japan is only because the Japanese surrendered to the USA
5. USSR gained the whole East-Europe but Britain and USA got Italy and France (USA alone Japan) and USSR in the last month helped China in territory more than USA in Italy and France together
6. Hitlers army stopped 19km from Moscow because tanks had no fuel witch means that in if the Battle of El Alamein would be lost the war would be lost for the allies.
So I can tell that if the war would not have USSR, Britain and USA doing what they did we would see swastika flags everywhere on Earth.