There seems to be a lot of hot discussion on this tiopic, so lets start from the begining. In 1940 the United States wanted a series of rights in Britain's Carribean colonies in return for a number of obsolete American tin can destroyers. It can be argued that FDR and is progressive Demnocratic party saw Britains empire as inherently evil. Some of this view is a natural conclusion drawn from America's birth in the American revolution or rebellion depending on your point of view.
As a Canadian I also saw some Canadians (such as Prime Minister King saw this as a time to escape from the Britrish. King worked in the Unitewd States as their ideal. King went to several American universities and wsork for a time within the American civil service before returning to Canada.
FDR saw Britain's condition during the Second World War as a advantage to crack open the Pound`s trading sphere. Ignoring the fact that the America`s dollar sphere was based on the same operating system the American diplomatic corps pushed for the desolution of Britain`s trading system And Britain was in no position to fight the USA oin this. By the end of the war Britain was drained of most of her financial resources. Britain had told the US that she coundn`t support any longer the anti-cxommunist forces in Greece and that the United States had to fill in her place.
As for the United States abandoning east European peopler there coundn`t be anyway around it. Churchill place a sheet before Stalin showing the spheres of diplomatic domination. To quote a modern statement the Soviets had boots on the ground and there was very little that the United Kingdom and the United States could short of full war. Both theb UK and thew US sent in small military teams with little effect showing except the killing of these teams by oviet forces.
FDR was anti-imperialist to his core and tried to bind the UK ninto the dismantalling of the British Empire. He was assisted after this death by Britain`s Labour Party. Labour wanted out of India as soon as possible. So Britain pulled out of India with disasterous effects. Britain allowed for the dismantalling of Greater India with the creation of Pakistan. The British threw in their cards and left the scene. Those Labour ministers were never held to account for the results of their actions. British actions led to untold numbers of dead and the the movement of masses of people during the midnight hour.The effects of this is still with us today. Pakistan was meant to be a secular state instead of what it is today. I suspect Pakistan`s founding father is spinning in his grave considering what happened to his creation.
All in all the decolonisation of the British Empire is complex affair ands what has been stated above is very simple. The dismantling of Britain's African Empire is another chapter and the French and Dutch Empires have not been discussed at all.