After the end of the Cold War, the North Atlantic Treaty Organization (NATO) used its military capabilities for the first time in actual conflict. Since then, it has been acting regularly, either under a United Nations' mandate or not. This work presents the debate in the literature on the permanence of NATO after the end of the Cold War and analyzes its transformation and new role in a distinct world context. Alliance theory does not explain the persistence of such an arrangement. Regime theory, on the other hand, allows for NATO persistence in a changed context, provided that it is able to transform itself and adapt to new conditions. The data obtained are used to test the hypothesis that there is a recent decline in UN humanitarian activism, which would make room for new actors to work on the field of global security. The conclusion is that although there is a decrease in UN activity, it is not significant compared to the Cold War period. Thus, instead of a possible omission on the part of the UN, it is the need to justify the permanence of the transatlantic link in a new strategic scenario that rises as a key factor in explaining why NATO takes on this interventionist and expeditionary character, quite distinct from its original one. The legitimacy NATO could have or lack for this type of missions is also part of the discussion. Finally, it is stressed here that legal problems of NATO action vis-à-vis the UN are included in an overarching question: the need for review of global collective security arrangements and of the Security Council, particularly.
NATO; International Security; International Intervention; UN Security Council
