Initially, the reciprocal defence obligation under Article 5 of the treaty could be triggered in five geographic scenarios. First, the obligation could be made by attacks on the territory of one or more signatories, provided that these territories are located in Europe or North America. Overseas territories, with a thesis on the North Atlantic islands, were excluded. Secondly, attacks were taken on an exceptional basis against the Algerian departments of France. Thirdly, attacks on the occupying forces of any party in Europe could also trigger mutual assistance, even if these forces were attacked outside their own territory. Fourth, the North Atlantic islands were covered north of the Tropic of Cancer. This means that the obligation of mutual defence extends to Greenland, but not to Hawaii. Finally, attacks on ships or aircraft in this area of the North Atlantic have also been covered by the mutual assistance guarantee. At Turkey`s request, NATO has implemented collective defence measures three times: in 1991 with the deployment of Patriot missiles during the Gulf War, in 2003 with the agreement on a set of defence measures and the implementation of Operation Display-Dissuasion during the Iraq crisis and in 2012 in response to the situation in Syria with the deployment of Patriot missiles.
When Article 5 was drafted in the late 1940s, there was consensus on the principle of mutual assistance, but there were substantive differences of opinion on how to implement this obligation. European participants wanted to ensure that the United States automatically came to the aid if one of the signatories was attacked; the United States did not want to make such a commitment and obtained that this was reflected in the text of Article 5. This article is supplemented by Article 6, which states that, although the North Atlantic Treaty is not directed against a particular adversary, its original purpose was to unite its signatories to face the threat of the Soviet Union. This objective gave rise to two general criteria for membership: NATO was to be a community of nations sharing common democratic ideals, but the involvement of a country also had to have a military and strategic meaning. As a result, NATO was conceived as an organization that has regional rather than potentially universal membership. As recognized in the Washington Paper of September 1948, the first detailed outline of what later became of the North Atlantic Treaty: “You have to draw a line somewhere” when it came to the geographical extent of NATO and its activities. Contracting parties may unanimously invite any other European state capable of supporting the principles of this treaty and contributing to the security of the North Atlantic to accede to this treaty. Any state so invited can become a party to the treaty by filing its instrument of membership with the government of the United States of America. The Government of the United States of America informs each of the contracting parties of the filing of any accession instrument. The following twelve states signed the treaty and thus became founding members of NATO. Finally, it is important to note that the geographical conditions imposed by Article 6 of the North Atlantic Treaty apply only. (c) the obligation of mutual defence under Article 5, and not to another provision of the agreement.