The Cold War has been a subject of interests of scholars for years. The first great debate concerned the causes of its emergence. Traditionalists saw them in the aggressive behavior of the Soviet Union, aimed at conquering Eastern Europe and Asia, which the United States had to resist. The policy of containment was a symbol of this counteraction. For revisionists, it was the intention of the US to dominate the international system, and the economic interests above all that caused certain actions due to which the USSR came under pressure and had to retaliate. Although the traditionalist concept was initially dominating, the acceptance of the second one has increased since the Vietnam War due to the criticism of the US policy at that time. Those two interpretations of the origins of the Cold War were reinterpreted under the new "neo" terms. The development of research and access to the archive were particularly important here. The second great debate concentrates on the causes of the Cold War ending. Those factors are discussed in terms of president Reagan's policy, transformations within the international system, the Gorbachev reforms and changes in the foreign policy concerned with the surprising and peaceful withdrawal from the Eastern Europe, consent to the unification of Germany, and the independence of the former republics. None of the theories of International Relations (IR) have anticipated such outcome. Although realism was criticized the most, other theories have not have not been able to grasp this phenomenon either. They failed by not asking the right questions, by not taking advantage of the growing number of data, by limiting themselves to one­‍‑sidedness, excessive reductionism, and as if out of habituation to a kind of unchangeable dichotomous world. Nevertheless, many scholars, addressing the issue of the IR theories’ significance, have pointed out that forecasting is not their aim, and therefore, not meeting such expectations does not make them ineffective in researching international relations.