What are some developments from 1941 to 1949 that increased suspicion and tension between the US and the USSR?

Question

What are some developments from 1941 to 1949 that increased suspicion and tension between the US and the USSR?

Answer 1

The capacity for nuclear weapons is a big one. Both nations were racing toward the development of the atomic bomb, the US got the technology first and obviously demonstrated the weapon's power at Nagasaki and Hiroshima. The USSR struggled to obtain the same capability but was unable to do so until the end of the 1940s. An interesting sidenote: the British philosopher Bertrand Russell (as well as others) called for the United States to use its newly obtained nuclear armament to force the USSR to join with the USA to form a world government and effectively end all major wars. He said that if the USSR did not agree that the US should launch a pre-emptive nuclear strike so as to prevent the USSR from obtaining nuclear weapons and making full-on nuclear war possible. What makes this really interesting is that Russell was a noted pacifist and served a prison sentence in Britain in WWI for criticism of his country's involvement.

Some of that is rather tangential to your question, but nuclear arms were certainly a major source of tension and suspicion between the USSR and the US in the years directly following WWII.