This paper aims at analyzing the globalization of NATO's military missions since the end of the Cold War. It is thus more precisely aimed at the panel on “Transatlanticism in Theory and Practice - Its Past, Present, and Future”. More precisely, the focus here will be put on the dialectic between international law and political practice to show how an international security organization as NATO relies on the practice of Chapter VII of the UN Charter to legitimize its globalization and conduct more and more out of area missions since the end of the 1990’s. The argumentation will focus on the case of NATO’s mission in Afghanistan (ISAF) since 2003 to show how an international security organization can induce a marginal change without changing its fundamental elements (the North Atlantic treaty has not been reformed to fit with NATO’s new tasks in crisis management). There international law constitutes an interesting political resource for NATO to push forward its globalization process. On a theorical level, we will rely on an analysis based on historical and sociological institutionalism to study how NATO as an international organization tries to cope with the new security challenges raised in the post Cold War era. We will confront this theory with the realist analysis often provided to explain NATO’s continuity after 1991, and show that institutionalism provides a very interesting and stimulating research agenda by focusing both on the organizational but also on the internal levels of the countries. We will then provide some examples of actors and arguments driving NATO’s globalization process both in some European countries security policies (mainly France and Germany here, as we studied both countries security policies towards transatlanticism). The final aim will be to understand how transatlanticism copes with the new challenges to international security in the 21st Century.