After 9/11, NATO invoked Article V and declared its readiness to come to the assistance of the US. This was a type of Article V engagement very different from any foreseen in 1949 or during the Cold War. NATO engaged in the surveillance and protection of the US homeland and in military operations in Afghanistan to prevent that country from remaining a safe haven for international terrorism. The Alliance had already assumed new roles and tasks in the 1990s, including crisis management and cooperative security, as described in the Strategic Concept of 1999. 1 Collective defence, however, is the only task directly based on the 1949 North Atlantic Treaty and thus binding on all member states.