alternatehistory.com

The McMahon Act was a piece of post-WW2 legislation governing American nuclear policy with the rest of the world. When it was passed in 1946, British access to information from the Manhattan Project was halted, and it effectively ended American and British nuclear cooperation until the late 1950s. It was a slap in the face to the British, and led to the establishment of an independent UK nuclear program.

But in large part, the Act seems to have arisen out of the chaos in the aftermath of Roosevelt's death. Apparently, much of the paperwork dealing with the various Anglo-American agreements on nuclear technology were lost - one of the biggest backers of the bill, Senator McMahon himself, said that if they had known about these agreements, the bill never would have existed.

So, let's say that things are a little more orderly for the incoming Truman administration - the existence of the Quebec and Hyde Park Agreements is known in Washington, and the McMahon Act never takes place. What affects would this have on relations between America and Britain, and the early Cold War?
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