NATO (the North Atlantic Treaty Organization) is an international alliance that consists of 28 member states from North America and Europe. It was established at the signing of the North Atlantic Treaty on 4 April 1949. Article Five of the treaty states that if an armed attack occurs against one of the member states, it should be considered an attack against all members, and other members shall assist the attacked member, with armed forces if necessary.
Of the 28 member countries, two are located in North America (Canada and the United States) and 25 are European countries while Turkey is in Eurasia. All members have militaries, except for Iceland which does not have a typical army (but does, however, have a coast guard and a small unit of civilian specialists for NATO operations). Three of NATO's members are nuclear weapons states: France, the United Kingdom, and the United States. NATO has 12 original founding member nation states, and from February 18 1952 to May 6,1955, it added 3 more member nations, and a fourth on May 30,1982. After the end of the Cold War, NATO added 12 more member nations (10 former Warsaw Pact members and two former Yugoslav republics) from March 12, 1999 to April 1, 2009.
NATO has added new members six times since its founding in 1949, and since 2009 NATO has had 28 members. Twelve countries were part of the founding of NATO: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States. In 1952, Greece and Turkey became members of the Alliance, joined later by West Germany (in 1955) and Spain (in 1982). In 1990, with the reunification of Germany, NATO grew to include the former country of East Germany. Between 1994 and 1997, wider forums for regional cooperation between NATO and its neighbors were set up, including the Partnership for Peace, the Mediterranean Dialogue initiative and the Euro-Atlantic Partnership Council. In 1997, three former Warsaw Pact countries, Hungary, the Czech Republic, and Poland, were invited to join NATO. After this fourth enlargement in 1999, the Vilnius group of The Baltics and seven East European countries formed in May 2000 to cooperate and lobby for further NATO membership. Seven of these countries joined in the fifth enlargement in 2004. Albania and Croatia joined in the sixth enlargement in 2009. Due to the 2016–17 Turkish purges and Turkey's turn to authoritarianism some have speculated that Turkey could be expelled from NATO.