Many people don't realize in World War 2, America's stupidity actually helped everyone.
America waited such a long time before joining in the war. The Axis powers almost had Britain defeated, and if Britain was gone the rest of Europe didn't stand a chance. The Soviet Union would of been alone against Germany, making them a easier target with only one front.
But, when the Americans did finally join in, they protected the British, doing this made sure that the Axis needed 3 fronts, and it also made them increase troops on the British front because they knew they were weakest link, making their defense against US and USSR a lot weaker. Which was vital reason to keep them around. And with America now attacking on another front, Soviet Union could more easily defend itself as GErmany was spread out on 3 fronts.
Eventually as the Allies closed in the Axis could not hold and fell, as many of the camps officers retreated inward or surrendered.
But...if you think of it on other terms, if America never joined in, Britain would of fallen and so would USSR, leaving Western Hemisphere open for easy one front access again.
So...in these terms, did the British win? No. Did the Soviets win? No Did America win? No.
Did the Allies together win? YES!