Here's a look at the North Atlantic Treaty Organization (NATO), headquartered in Brussels, Belgium.
Facts: The organization's charter states that the signing parties affirm the principles of the United Nations charter, will "seek to promote stability and well-being in the North Atlantic area", and will "unite their efforts for the collective defense and for the preservation of peace and security."
April 4, 1949 - Established when 12 nations sign the North Atlantic Treaty in a ceremony in Washington, D.C.
2009-present - The current secretary general is Anders Fogh Rasmussen of Denmark.
28 Member Countries: Albania (2009) Belgium (1949) Bulgaria (2004) Canada (1949) Croatia (2009) Czech Republic (1999) Denmark (1949) Estonia (2004) France (1949) Germany (1955, as West Germany) Greece (1952) Hungary (1999) Iceland (1949) Italy (1949) Latvia (2004) Lithuania (2004) Luxembourg (1949) Netherlands (1949) Norway (1949) Poland (1999) Portugal (1949) Romania (2004) Slovakia (2004) Slovenia (2004) Spain (1982) Turkey (1952) United Kingdom (1949) United States (1949)
Timeline (selected): April 4, 1949 - The 12 nations of Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the United States, sign the North Atlantic Treaty in Washington, D.C.
July 25, 1950 - First meeting of NATO Council Deputies in London. U.S. Ambassador Charles M. Spofford is elected permanent chairman.
December 19, 1950 - General Dwight Eisenhower is appointed the first supreme allied commander.
April 2, 1951 - Allied Command in Europe becomes operational with Supreme Headquarters Allied Powers Europe (SHAPE) in Roquencourt, near Paris.
March 12, 1952 - Lord Ismay is named the first secretary general of NATO and appointed vice chairman of the North Atlantic Council.
April 10, 1952 - Allied Command Atlantic (ACLANT) becomes operational, headquartered in Norfolk, Virginia.
April 16, 1952 - NATO establishes its provisional headquarters in Paris at the Palais de Chaillot.
April 28, 1952 - First meeting of the North Atlantic Council in permanent session in Paris.
May 6, 1952 - West Germany joins NATO.
May 14, 1955 - The Soviet Union and Eastern Bloc countries form the Warsaw Pact in response to West Germany joining NATO.
July 26, 1956 - Egypt nationalizes the Suez Canal. France and Great Britain use troops to intervene, against the wishes of the United States, causing a rift in NATO.
August 13, 1961 - The Berlin Wall is erected.
October 22 -23, 1963 - NATO and the United States demonstrate the size and speed of emergency forces with 14,500 U.S. troops flown into West Germany for maneuvers.
March 10, 1966 - France formally announces intentions to withdraw from the military structure of NATO, accusing the United States of having too much influence in the organization.
March 31, 1967 - Opening ceremony of new NATO headquarters in Casteau, near Mons, Belgium in Brussels.
August 14, 1974 - Greece, angered at NATO's response to the Turkish invasion of Cyprus, withdraws from the military arm of NATO.
October 20, 1980 - Greece rejoins the NATO military structure.
May 30, 1982 - Spain joins NATO.
November 9, 1989 - The Berlin Wall comes down.
October 3, 1990 - Germany is reunified after 45 years. With German reunification, East Germany leaves the Warsaw Pact and is incorporated into NATO.