The document summarizes key events in the development of the Cold War between 1943-1956:
1) Tensions grew between the former allies US and USSR after WWII as their differing economic ideologies of capitalism vs communism emerged. This led to the breakdown of their wartime alliance known as the Grand Alliance.
2) A series of conferences between the US, UK, and USSR failed to resolve disagreements over postwar Germany and Eastern Europe, with Stalin determined to establish communist control over a buffer zone.
3) The development of nuclear weapons by the US emboldened Truman in dealings with Stalin but also escalated arms races and tensions between the two superpowers, ushering in the Cold War era.