집단방위 (나토 조약 제5조, 핵심조항)
동맹국 일방에 대한 무력공격을 전체 동맹국에 대한 공격으로 간주, 피침국에 대해 (필요시 무력사용을 포함한) 원조 제공
Article 5 : 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-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.
NATO는 동 조항을 2001.9.11 테러사건 후 최초로 원용, 미국에 대한 원조제공 의지표명
적용범위 : 유럽 및 북미 동맹국 영토에 한정