The September 11 attacks in the United States caused NATO to invoke Article 5 of the NATO Charter for the first time in the organization 's history . The Article states that an attack on any member shall be considered to be an attack on all . The invocation was confirmed on 4 October 2001 when NATO determined that the attacks were indeed eligible under the terms of the North Atlantic Treaty . The eight official actions taken by NATO in response to the attacks included Operation '' Eagle Assist '' and Operation '' Active Endeavour '' , a naval operation in the Mediterranean Sea designed to prevent the movement of terrorists or weapons of mass destruction , and to enhance the security of shipping in general , which began on 4 October 2001
September 11 attacks
September 11 attacks
NATO