Why was Stalin upset at the US?

Stalin was upset with the US for several reasons, primarily stemming from the perceived betrayal of trust during and after World War II. He felt that the US delayed opening a second front in Europe, which led to unnecessary Soviet casualties. Additionally, the onset of the Cold War and the US's promotion of capitalism contrasted sharply with Stalin's communist ideology, heightening tensions. Lastly, the US's atomic bomb development and subsequent use against Japan fueled Stalin's fears of American intentions and military dominance.