NATO has two official languages, English and French, defined in Article 14 of the North Atlantic Treaty. For English, NATO uses British English spelling. This is said in its online frequently asked questions (FAQ): "Q: Why do you spell 'organisation' with an 's' and not a 'z'? A: By tradition, NATO uses European English spellings in all public information documents...".
Its members in the beginning were: The United States, Belgium, the Netherlands, Luxembourg, France, the United Kingdom, Canada, Portugal, Italy, Norway, Denmark and Iceland. Three years later, on 18 February 1952, Greece and Turkey also joined.
In 1954 the Soviet Union suggested that it should join NATO to preserve peace in Europe. The NATO countries did not agree as it would destroy the purpose of NATO.
When West Germany joined the organization on 9 May 1955 it was described as "a decisive turning point in the history of our continent" by Halvard Lange, Foreign Minister of Norway at the time. Indeed, the result was the Warsaw Pact, signed on 14 May 1955 by the Soviet Union and its satellite states as response to NATO. This hardened the positions of the two opposing sides of the Cold War.
After the Cold war in 1999 three former communist countries, Hungary, the Czech Republic, and Poland joined the NATO. On 29 March 2004 seven more Northern European and Eastern European countries joined NATO: Estonia, Latvia and Lithuania and also Slovenia, Slovakia, Bulgaria, and Romania.
Croatia and Albania received NATO membership invitation on 3 April 2008. Republic of Macedonia received only conditional invitation because it was vetoed by Greece due to FYROM's name dispute with Greece.