9/11 (September) is one of the influential events in the international politics. In fact this event opens a new chapter of transaction in international relation and has been affected great powers policy and international institution in different aspects. NATO as the most important security institution in West also affected by these events. These events have been changed NATO strategy in deal with of threaten to West security. Among this 9/11 has been changed NATO enlargement process.
This article examines survival and continue of NATO after the cold war trough Neorealist and Neoliberal Institutional theory, and the changes that 9/11 have in relations of transatlantic countries and Five Provision of NATO and also affects of this changes on NATO enlargement process.