George Kennan believed that the Soviet Union's past experiences, particularly its traumatic experiences during World War II and earlier conflicts, created a deep-seated sense of insecurity and fear among its leaders. This led to a defensive and aggressive posture towards the outside world, as they viewed the West as a potential threat to their security and survival. This worldview was reflected in the Soviet government's policies and actions during the Cold War, such as the development of nuclear weapons and support for Communist movements.