// Just imagine if we hadn't been there from the off....and for the duration. //
the UK leaving early was a real possibility. after chamberlain was humiliated into resigning in May 1940 the favorite as his successor was Halifax, who favoured negotiating peace, particularly in the face of the developing disaster at Dunkirk. but he declined and Churchill became pm. Churchill was against negotiating but couldn't just reject that stance as although pm, he wasn't party leader so had to sell his "fight on" policy by persuasion. as late as the end of May, negotiation was still being discussed, as a means of protecting the empire.
what if the uk had negotiated? with the war in the west suspended (with UK neutralised and the Italians remaining neutral), the Nazis would have been able to fling all their resources eastwards into a resounding defeat of the soviets. Britain would have preserved the empire but in the face of a rampant germany, would have been unlikely to have retained it for long after hostilities ended. and with Britain no longer fighting, the US would have been unlikely to get itself involved in Europe and pursued its "America First" policy in defending its pacific interests from the Japanese.