And without US involvement, and knowing that the British could never have launched a D-Day type invasion on their own, the Germans could have kept a far smaller presence in France, which would thereby have allowed them to concentrate overwhelmingly on defeating the USSR.
Once Hitler was forced to engage in monumental struggles for existence on both his eastern and western fronts simultaneously, the end was never really in doubt.
75 years ago this week, the British army stood on the brink of disaster.
Routed by the Nazi blitzkrieg, and facing annihilation in a town in Northern France, most of the troops escaped in what some called a miracle.
Churchill was surely right to declare that 1940 was the British people's "finest hour", as they resisted the Nazis alone.
But key to British success and survival were the four unforced errors committed by the Fuehrer.The second two mistakes, even more significant in global terms, took place in 1941 and ensured Hitler's eventual defeat as he brought first the USSR and then the USA into the war on Britain's side.As their French, Dutch and Belgian allies collapsed before the German onslaught, the survivors of the British Expeditionary Force retreated to the channel port of Dunkirk.But with the Royal Air Force again outnumbered, and its losses mounting dangerously, Hitler suddenly instructed the Luftwaffe to shift bombing targets away from the airfields of the beleaguered RAF to London and other cities.So at this pivotal moment, RAF Fighter Command was granted time to recover and regroup, allowing its pilots to continue their heroic defence, and the Battle of Britain was won.On hearing the news, Churchill said he "went to bed and slept the sleep of the saved and thankful". After all, the Japanese attack indeed ensured that the US would go to war – but only against Japan.Without Hitler's wholly gratuitous declaration, the Roosevelt Administration would never have persuaded Congress to go to war in Europe instead of focusing on the Pacific.With their backs to the sea and on the brink of obliteration by the vastly superior Luftwaffe and Wehrmacht, the British were saved by what must be the most remarkable evacuation of modern times.In "Operation Dynamo", the Royal Navy – assisted by hundreds of private fishing boats, life-boats and yachts from England (200 of which were sunk by German air attacks) – ferried to safety a third of a million British and French soldiers.If this was part of his reasoning, it was an epic misjudgment of his opponent's national psyche.Had all the British soldiers at Dunkirk been killed or captured, the nation would have been utterly traumatized, and it is hard to imagine that the British have been able to resist for long.