Due to the lack of vision concerning the future evolution of the international system, there was little agreement on how to actually proceed in reestablishing and redefining the role and scope of NATO. This is why some scholars considered that the immediate years following the end of the Cold War were marked by a high degree of uncertainty arguing that the aims set forth in 1991 were vague and without a clear determination in time and space (Foster and Williams, 2001). The leaders of the Alliance needed, according to the realist and neorealist vision a new common threat or common goal that would keep the Cold War unity unchanged. In this sense, Europeans considered the cooperation with the U.S. To be security insurance, while the American side viewed NATO as a means to exercise its influence in terms of security in general (Cottey, 2004). This in turn would lead to the maintenance of unity inside the Alliance. Despite the theoretical aspects, the main result of this time of searching was the continuity NATO experienced immediately after the Cold War.

The institutionalist approach, unlike the neorealist one, takes into account different aspects of the institutional theory. According to these beliefs, institutions are essential for the establishment of a world order. On the one hand, because they represent the actual framework of the conduct of international relations and, on the other hand, because they set up certain rules and formulate behavior criteria which ensure a peaceful and positive development of the world (Nye, 2005). In the institutional theoretical framework, the role of organizations and regimes is that of providing choices and incentives. Such actions can be used as an alternative means of changing the political and international environment, an alternative to war.

The use of institutions with this aim is the result of the fact that "institution-building has been intimately tied to strategies of learning and change, of changing the economic fabric of a society" (Reinert, 2006). By applying a different set of norms, or by conducting a policy aimed at cultivating cooperation inside various institutions, the entire international system can change to such an extent as these institutions can set the future distribution of power, and even define regional identities and roles (Nye, 2005; Scharpf, 2000). The Partnership for Peace established by NATO in 1994 was the expression of this approach (Borawski, 1995). An American initiative, this step was taken as a result of the consideration of the possible future relations with the former Soviet satellites. In this sense, NATO was used as a means to offer incentives and opportunities for engagement in international politics with the expressed aim of changing the world order as it had been until the end of the Cold War. From this point-of-view, it can be said that the institutional approach was used as guidance for the establishment of the new set of goals of the organization.

The institutional theory has, as any other international relations theoretical approach, a series of secondary lines of though. However, for the study of international politics, rational choice institutionalism appears to be the most appropriate. NATO's attitude in the early 1990 regarding the expansion of the Alliance to include Eastern and former communist countries can be explained through the rational choice approach. In this sense, "an actor's behavior is likely to be driven, not by impersonal historical forces, but by a strategic calculus and (...) this calculus will be deeply affected by the actor's expectations about how others are likely to behave as well. Institutions structure such interactions, by affecting the range and sequence of alternatives on the choice-agenda or by providing information and enforcement mechanisms that reduce uncertainty about the corresponding behavior of others and allow 'gains from exchange,' thereby leading actors toward particular calculations and potentially better social outcomes" (Hall and Taylor, 2006). Thus, the United States, in order to ensure that it builds an influence in former communist countries and promotes a different set of values and norms in order to replace the Soviet ones, advanced a project meant at increasing the cooperation with states outside NATO in the perspective of membership, thus helping them to reemerge as political actors in Europe and strengthen their strive for democracy (Borawski, 1995; Walt, 1998).

The third approach to the evolution and development of NATO came in the form of social constructivism. In general, the theory argues a different position on international politics, the balance of power, security issues, state identity and state interest (Hopf, 1998). Unlike neorealist views and institutional ones, social constructivism "rests on an irreducibly intersubjective dimension of human action (...) in short, constructivism is about human consciousness and its role in international life" (Ruggie, 1998). One of the most important authors of social constructivism, Alexander Wendt...

Therefore in order to establish some kind of international order, it is important to focus on the actual process and to take into account the actors which are able to change the current state of affairs.
From the late 1990s NATO faced an increasingly new types of threats related to the issue of national interest and different wars going on the European continent (Helsing, 2000). The 1991 Yugoslavian war, the Bosnian crisis, the Kosovo crisis all represented challenges NATO had to face if, from the point-of-view of the social constructivist theory, it were to have a role in the future architecture of international relations. The so called collective security issue was defined especially during the Balkan wars (Frederking, 2003). Moreover, the 9/11 events have represented a great challenge for the international system due to the variety of threats posed by terrorism (Gordon, 2001-02; Cornish, 2004). In this sense, constructivism believed that institution and actions taken at an international level have the power and ability to change the international scene. Therefore, although they did not deny the existence of anarchy, they argue that such a state of being can be changed. Similarly, NATO, through its actions that developed away from being solely a military alliance, but also a democracy building one, can change the state of affairs in different countries or regions (Cornish, 2004). It may be that it is precisely this new target and this new orientation of goals and aims which keep NATO alive.

This approach taken into consideration, NATO has adopted a new system of strategies ever since the 1991 Summit of Rome (Croft, 2000). These include cooperation with other organizations such as the OSCE, the UN, and the EU in particular (Boulden, n.d.; Sznyi, 1997)