Hand in it?

They damn near required it.

I forget the name of the treaty, but FDR gave Churchill an ultimatum: American involvement in the war would require Britain to cede all technological and intelligence information that the British possessed. Churchill would have known even at that time, there was basically no chance the British Empire could keep up with the shocking industrial might of the US, and this was still at a time where most Americans were still rural. Then, they were going to give all of their technological knowledge to them. It meant that the US was certain to be the global hegemon going forward; something the Europeans had been (frankly) expecting since the late 1800's prior to WW1, and weren't really sure how to handle it. With Germany on the loose, National Socialism having allies in Scotland, Ireland staying out of the war, France already collapsed faster than anyone predicted (even the Germans), and England genuinely under threat of invasion, it looked like he had no other choice but to guarantee the loss of the majority of the British Empire in order to save any of it.

After that, the American government (having seized their own citizen's gold supply), also became the world reserve currency because they were really one of the only developed countries to have had a massive supply of gold and not suffered massive structural damage during the war. They became a creditor nation to every country in Europe, guaranteeing that there was no chance anyone from Europe could take the Americans on... but jesus-christ-almighty that's better than the looming threat of Soviet conquest of Europe. The Soviets may have been utterly exhausted by 1945 with twenty million dead, but they were still an active and ongoing threat.

But, the Americans weren't the only cause. Fabian Socialism had been developing very well in England prior to WW1, and when Churchill lost his election, the Socialists seized power in Britain, and there was no chance the Empire could be saved, because it was their goal to destroy it. They had allies in the US State Department (and still do), but it's not like the Americans wanted Britain to lose the war. The Labour Party absolutely would have preferred that Britain lose the war because she 'deserved it'. Even Orwell noted this.