The North Atlantic Treaty Organization (NATO) responded to the terrorist attacks on the United States because its charter states that an attack on any member nation is considered an attack on the alliance. The language is contained in Article 5 of the NATO Treaty, signed April 4, 1949, in Washington, D.C.: “The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defense … will assist the Party or Parties so attacked.” It was the first time Article 5 had been invoked by NATO since its founding.

On September 12, 2001, NATO convened a special meeting in response to the attacks on American soil and afterward issued a statement saying, in part, that the United States could rely on the support and assistance of NATO if it was found that the attack was directed from abroad. The organization’s secretary general, Lord Robertson (1946-), strongly condemned the attacks and called for the “international community and the members of the Alliance to unite their forces in fighting the scourge of terrorism.”

The invocation of Article 5 was confirmed by NATO on October 2, after U.S. Ambassador-at-Large Frank Taylor briefed the organization’s chief decision-making body on the investigations into the terrorist attacks. The North Atlantic Council determined that the information provided by Taylor confirmed that “that the individuals who carried out the attacks belonged to the world-wide terrorist network of Al-Qaida, headed by Osama bin Laden and protected by the Taleban regime in Afghanistan.”

At a press conference held October 8, Secretary General Lord Robertson announced NATO’s full support for the U.S.-led invasion of Afghanistan. The following day it was confirmed that NATO assets had been deployed to the eastern Mediterranean to establish a presence in the region. But the alliance did not take a lead role in the military effort to oust the Taliban from Afghanistan.