I still think that the USA saved europe from certain demise. Aside from the provisions supplied to England, and the USSR, think of the tremendous battles that took place on the pacific front.
If the size and scope of the battle equates to its importance, then every WW2 battle performed by every other participants of WW2 is absolutely dwarfed in scale against what the Germans and Russians were doing in the Eastern front between '41 and '44. With a bit of exaggeration, a single day of battle in Stalingrad '42, outdoes the entire Normandy Landing of '44, in the scope of ferocity and viciousness, with each side locked in a catastrophical fight quite uninmaginable to even the most seasoned veterans of the Western Allies.
Again, I'm not trying to belittle the war effort of the USA in WW2... but just what kind of grave and utmost importance the USSR held in turning the entire tide of war in WW2 still goes way unnoticed, even up to this date when the Cold War has been finished for nearly two decades.
Eliminate the USA from the equation, and Japan would have been able to eventually send support to there allies.
I sincerely doubt the possibility of this ever happening. Even before the US entered the war in the Pacific the Japanese advancement was meeting a critical limit due to the lack of manpower, resources, and fore-planning. It is said that the Japanese high command was actually in confusement as to what to do next - since they've already reached South-Eastern Asia much too quickly. Some Japanese strategists suggested sending reinforcement troops across India and Middle East to North Africa, but this idea was quickly rejected as being technically inplausible according to the current state of the Japanese military.
The entire front was stretched out too thin and signs of problems in maintaining it was becoming more and more clear. It is at this point the US threathened to cut off important strategical resources - which would prove catastrophic for the Japanese in maintaining their already fragile extent of the Empire. That crossed the final line of patience the Japanese held.
Then consider what's been mentioned about airpower. Although the lancasters did do damage, they didnt have a never ending supply of them, and think what would have happened if you eliminate the American bombing factions, not to mention wildcats, hellcats, hogs, jugs, mustangs etc. No Patton to help Monty stop Rommel in a country rich with resources.
The germans would have still been able to get supplies to both fronts and things would have been ALOT different.
However, beating down German airpower in the defensive was no picnic either. With the bulk of its military resources allocated in the Eastern front the Luftwaffe was still powerful enough to cause such high loss rates to the US bombing campaigns that the entire daylight bombing raids were halted for a period. The survivability of a bomber crewman was becoming dangerously low for the US and as a result they had to redevise the entire bombing tactics to something that was much safer, with reduced accuracy in bombing compensated only by a massive number of bombs dropped - and despite this threat the German economy was still reaching its peak in production rates well up to 1944. Ofcourse, such production under war pressure would prove ultimately suicidal for a single country's overall economic structure, but the point is they were still making more planes in 1944 when the US was bombing the hell out its industry, than they were in 1941 when they were on the offensive.
Unending fights in the skies over France and West Germany no doubt cost a certain amount of skilled pilots for the Germans, but in that aspect the fights over Russian soil also caused as much - if not more - losses to the Luftwaffe pool of manpower. Detailed accounts of German aces such as Grislawski describes how the Eastern front in 1943 was nothing like he rememberd in 1941 - he actually suggested his friend from the training camps that he'd make some phone calls to have his friend moved to his own squadron where he could 'protect' him, and ensure his survival for at least 50 missions. Grislawski goes so far as to comment that every single pilot his friend will fly with, will be dead in two weeks, and the only way he could survive was by flying with himself.
If you want to take it a step further, imagine if the USA stayed totally out of the war on all levels from the beginning, and pearl harbor never happened?
If the 'all levels' includes aids in the form of economic leases of materials and supplies then I admit that I believe the war might have been victorious for the Germans.
However, concerning military intervention alone, the WW2 would still have been victorious for the Allies even without the US forces in the ETO or the MTO. Like joeblogs said, the tide of the war was already turned by the Red Army, long before the US landed on Omaha beach. When the US was just beginning the bombing raids on a worthy scale in 1943 the Soviets were on a series of decisive counter attacks in the aftermath of operation Uranos, follwed by Saturn. The German offensive at Kursk, Operation: Zitadel, proved fatal in the bloodiest tank battles in history of mankind and the road to Germany's doors were pried open by the Red Army.
The Red Army needed no "surprise landings" at an unexpected spot to drive through enemy lands. They met the cream of the Wehrmacht head-on and still smashed through (although not without considerable number of casualties, even after the early years). By 1944, the Red Army proved to be strongest standing army the world has ever known, outperforming every army in the world, in the most advanced mobile infantry tactics which the Germans once boasted they were best at. The survivors of the bloody early years have been toughened to become the most effective and ruthless breed of veteran soldiers, and the terror both from the enemies and from the state has molded the Russian officers and commanders into brilliant tacticians, strategists, and leaders
Although USSR did not win WW2 single handedly (no country has single handedly wone the WW2), when it comes to determining who was the most decisvie force behind Germany's surrender, I vote for the USSR, hands-down.
