 The end of the Cold War completely changed the international security environment. With the demise of the Soviet threat, what was going to be the purpose of the Alliance? Would, indeed, NATO continue to exist, and why? This video will outline the redefinition of the Alliance at the end of the Cold War, while pointing to the main issues that shaped the making of NATO's new role in the post-Cold War era. Following the reunification of Germany in 1990 and the new German state remaining a member of NATO, the debate on the future of the Alliance rotated from the beginning around the issue of potential expansion eastward. NATO expansion, indeed, emerged as a key issue after the end of the Cold War. As US President George H.W. Bush put it, a new world order was taking shape, a new era, freer from the threat of terror, stronger in the pursuit of justice, and more secure in the quest for peace, an era in which the nations of the world, east and west, north and south, can prosper and live in harmony. NATO member countries, far from viewing their mission as finished, sought a new role for the Alliance, a more wide-ranging and active role in the pursuit of peace and stability in Europe and beyond. This test case for NATO's new role came during the Balkan Wars of the 1990s. As war broke out in the former Yugoslavia, the Alliance issued a statement urging all parties to allow the deployment of UN peacekeepers. This was the beginning of a partnership between NATO and the UN in seeking to bring hostilities to an end. NATO then intervened directly in the conflict with airstrikes, authorized by the United Nations. Following the date and accords of 1995, the Alliance first deployed peacekeeping forces, I-S-4, and later a stabilization force, S-4, which remained in the country until 2004. Similarly, when tensions in the Balkans re-escalated in Kosovo, NATO rapidly intervened with an air campaign under UN Security Council mandate, aimed at bringing the violence to an end. A peace support operation, CASE-4, was deployed in 1999 and, under renewed mandate, remains in Kosovo to this day. Clearly, the Alliance had evolved into a new player, seeking to be a force for peace and stability in the new post-Cold War world. Concurrently, the Alliance reached out to non-member states through the Partnership for Peace, launched in 1994. This was and is a program of bilateral cooperation between individual Euro-Atlantic partner countries and NATO. It allows partners to build up an individual relationship with NATO, choosing their own priorities for cooperation. The Alliance's new role was clearly spelled out in the new strategic concept of 1999. The year of NATO's 50th anniversary, Allied leaders adopted a new strategic concept that committed members to common defence and peace and stability of the wider Euro-Atlantic area. It was based on a broad definition of security, which recognised the importance of political, economic, social and environmental factors, in addition to the defence dimension. It identified the new risks that had emerged since the end of the Cold War, which included terrorism, ethnic conflict, human rights abuses, political instability, economic fragility and the spread of nuclear, biological and chemical weapons and their means of delivery. The broader and more global role played by the Alliance was reflected in the successive enlargement rounds, starting in 1999 when the Czech Republic, Hungary and Poland became members of the Alliance, and with an even greater enlargement in 2004, when seven more countries entered the Alliance, NATO almost doubled its membership of 1949. Far from being an alliance in demise, NATO was becoming bigger and bigger and seemed to have a growing importance in the post-Cold War era. The significance and continued relevance of the Alliance was confirmed in the immediate aftermath of the September 11, 2001 attacks on the United States. Confirming the unity and purpose of its members, Article 5 of the North Atlantic Treaty was invoked for the first time in the history of the Alliance on September 12, 2001. An attack on the United States was considered an attack against all member states. The fact that the article had never been invoked during the Cold War, but was invoked in 2001, demonstrated that the Alliance was still needed, or perhaps because of a completely different security environment. The successive role played by NATO in Afghanistan, with the deployment of the International Security Assistant Force, ISAF, which remained in the country until 2014, confirmed the redefinition of the Alliance to include missions outside the territorial scope of the Alliance. The out-of-area dilemma which had plagued NATO during the Cold War had been resolved in favour of an acknowledgement that in the future, NATO had to act outside the Euro-Atlantic area to protect the territory of its member states. The crisis over the annexation of Crimea in 2014 refocused NATO on its more traditional purpose of deterrence and defence in its core territory. The crisis caused the most significant reinforcement of NATO's collective defence since the end of the Cold War, plus confirming that while the new and more global role of the Alliance was a defining feature of NATO's new role, the core mission of defending the Euro-Atlantic area remained at the centre of the Alliance's priorities. Alliance cohesion, particularly given the size of the Alliance, currently at 29 member states, as well as balancing the need to go out of area without undermining the defence of NATO's core territory, are among the main challenges the Alliance faced in the post-Cold War. Moreover, given the successive enlargements eastward to include in the Alliance countries formerly in the Warsaw Pact, raised issues on the uneasy relationship with the Russian Federation. Difficulties that had remained hidden and subdued until the crisis in Crimea dramatically brought them to the forefront. The future of the Alliance will rotate around the delicate balancing of these crucial issues. Alliance cohesion, balancing in and out of area commitments and the relationship with Russia.