I don't believe that's fair to say. The U.S. devoted considerable resources both during and after WWII to maintaining the UK. This included lend-lease aid, eventually direct military support, and the Marshall Plan following the war.
As a parallel point, the U.S. also devoted considerable aid to France following the war as well. In July 1950, in exchange for France allowing West Germany into NATO, the U.S. provided "substantial military aid" to French forces fighting in SE Asia. The point I'm trying to make here is: why would the U.S. deliberately try to fell British influence while enhancing French?
In any case, as I'm sure you're aware, it wasn't enough. In 1954, the U.S. gave up support because the French couldn't win the war. Then, in a fit of geopolitical genius (/s), America shortly afterwards got itself into exactly the same problem the French had and received the same result.
Now can you dig around and find some document from some member of the US government from 1926 speculating on the fall of Britain and how America could take advantage? Probably. But that's not why it happened.
What i'm getting at with all this is that the fall of the European empires following World War II was not because of the United States. They were simply too expensive to maintain at a time that Europe was struggling to provide for itself. The people that were ruled by Europe were not oblivious to this fact and took advantage to throw off the yoke.
Source: Postwar: A History of Europe Since 1945 by Tony Judt
Yes. Roosevelt, while often known for being on good terms with Churchill, and one of the architects of the 'special relationship' made a considerable effort to undermine Great Britain, especially prior to Dunkirk and the subsequent the Battle of Britain.
Roosevelt, and many of his inner circle, while ideologically opposed to fascism, were also nominally opposed to the imperialism that Britain represented, even if this were hypocritical to some degree.
Much of Britain's strength came from the sea, and subsequently, controlling global trade. While its navy was at a fifth of what it was at the start of WW1, it was still the largest navy in the world. Much of the negotiation between Britain and America in the first year of World War 2 revolved around Britain attempting to bolster is stretched naval force with fifty or so 'mothballed' destroyers the Americans had. Roosevelt would take a large political risk in lending them to the British, so used them as a bargaining chip: the British would have to guarantee that if the British Isles were invaded, its navy would sail to America. This was an extremely sore point for Churchill, as it would more or less symbolically hand reins of imperial order to America. Fortunately for him, it would not come to pass. Churchill never had to make that promise.
Representatives from Washington cabled the Prime-Minister of Canada on several occasions in order to try and convince him to make similar promises, or perhaps form a new military alliance with America. In general, there was a feeling in Washington that with Hitler in control of mainland Europe, the balance of power was shifting, and America would do what was best for America. The importance of sea-power should not be underestimated- and this passing of the torch was somewhat forcefully made from Britain to America.
However, the crisis of 1940 passed. Britain saved itself, and was able to rebuild its armed forces with American help. However, as vital as Britain was, the tension between America and the British remained and flared up over differences in the priorities of the war (reclaiming Europe versus retaking territory from North Africa, for instance).
After the invasion of Europe in 1944; the composition of the Allied forces shifted sharply in favour of the Americans, and it became clear that they would now be shouldering the burden (and reaping the rewards) of being the 'the more equal' of the two partners. While the British were still nominally an equal partner at delegations, they no longer had the largest navy. Many of their territorial possessions had in some ways traded their enthusiastic participation for a bargaining chip towards independence (such as India, which sent over a million volunteers).
Sources: The Finest Hour - Tim Clayton, Phil Craig. End of the Beginning - Tim Clayton, Phil Craig. Fatal Decision - Carlo De'Este. An Army at Dawn - Rick Atkinson.
Edited for grammar.
To clarify, as no one has replied yet: I am specifically thinking of post-war events like the Suez crisis, which some argue the US used to deliberately curtail British global influence. I was wondering if there were any events like that during WWII.
Of course any other material that is relevant is welcome. For example, were there any conversations within the US government about using lend-lease to exert control over the British, or was the motive entirely generous?
Question: Did the U.S. force the UK to open up markets and reduce tariffs that were traditionally used to close off the empire from outside markets? I recall hearing about something like this but a quick google search failed me.
The answer is quite simply no. It's quite frankly an invented narrative by those who are still in denial that the British Empire was essentially dissolved because of its own actions.
The key event in the dissolution of the British Empire - and the diminishing of British global influence - was the independence of India. And Roosevelt had almost no involvement in Indian independence. Roosevelt in fact had to back down from including a provision on Indian Independence in the Atlantic Charter at Churchill's insistence, and Indian writers would later lament that the Americans ultimately handed all control and responsibility over the issue of Indian independence to the British:
Nonetheless Indian independence went ahead due to these several key factors:
India was dragged into the Second World War despite opposition by Indian leaders.
The British were soundly defeated at Singapore, resulting in thousands of Indian soldiers being captured. Some, feeling abandoned by the British, eventually joined the anti-British "Indian National Army" fighting the Japanese.
The British essentially ignored a massive famine in Bengal that resulted in the death of millions.
The Indian Army and Navy mutinied in small scale against perceived injustices by the British military.
All of which were entirely British decisions and happened under the auspices of the Churchill government. The Atlee government which succeeded Churchill understood that the writing was on the wall and it was no longer possible to maintain British control over India; hence the granting of Indian independence in 1947 (with the disastrous India-Pakistan partition).
A similar and equally false narrative accuses Roosevelt of colluding with Stalin to reduce British influence in Eastern Europe. In reality, the British met with the Soviets secretly in October 1944 and concluded the "percentages agreement" - which gave the British control of Greece in exchange for Soviet control of the rest of Eastern Europe. The Americans, whose position had been to allow the self-determination of each Eastern European country, had been deliberately excluded from this meeting. And despite Churchill's later "Iron Curtain" speech, the Soviets in fact largely honored the agreement and allowed the British to keep Greece.
In short, it was not the Americans exploiting the Second World War to diminish British global influence. Instead the British in fact actively sought to manipulate America into preserving its own crumbling power and influence; due to its own bungling mismanagement of the colonies and bad deal-making with the Soviets. That this narrative isn't more well-known owes to Churchill's bloated post-war reputation due to his speeches and Britain's general denial that its empire was far from the progressive force the imperialists made it out to be.
Edit- spelling, grammar.
Not quite the US Gov but the OSS under Donovan were anti imperialist and spent as much time and money attempting to overthrow imperial holdings around the world as trying to win the war. Donovan had the ear of Roosevelt during the war and only lost political power/standing when Truman took over.
They were considered hostile by MI6 and SOE and banned by those organisations to operate in the BE.
Its not to say the British Empire fell due to US exploitation, But I don't think you can doubt a power change was recognised and the US took advantage of its new position, whilst personally being filled with anglo - phobes and philes.