The North Atlantic Treaty Organization was formed shortly after the end of the Second World War to counter the threat of Soviet invasion of Western Europe. The treaty setting up the alliance was signed in 1949 by 10 Western European nations as well as Canada and the United States. NATO's mandate is to provide a common defence for the European and Atlantic areas, and to address common issues faced by the member countries.

Membership (year of entry in brackets): Albania (2009)

Belgium (1949)

Bulgaria (2004)

Canada (1949)

Croatia (2009)

Czech Republic (1999)

Denmark (1949)

Estonia (2004)

France (1949)

(West) Germany (1955)

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)

As evidenced by Article One of the treaty, the authors took pains to respect and complement the principles of the United Nations charter, which was signed four years earlier:

"The Parties undertake, as set forth in the Charter of the United Nations, to settle any international disputes in which they may be involved by peaceful means in such a manner that international peace and security, and justice, are not endangered, and to refrain in their international relations from the threat or use of force in any manner inconsistent with the purposes of the United Nations."

Article Seven of the treaty emphasizes that UN Security Council responsibility for international peace and security will always take precedence over any NATO obligations.

From its founding until the fall of the Berlin Wall in 1989, NATO embodied the ideals of the democratic West opposed to the Communist East Bloc nations under the Soviet Union.

With the end of the Cold War, NATO was forced to change to suit the times. NATO was heavily involved in the conflicts that consumed the former Yugoslavia in the 1990s. In 1995, NATO troops were dispatched to Bosnia to enforce the peace. In 1999, NATO warplanes conducted 11 months of bombing raids on Yugoslavia in a bid to end attacks on ethnic Albanians in the province of Kosovo. It was the first time NATO acted without UN authorization.

Structure

NATO is composed of a political and a military structure. The political component is based in Brussels, Belgium. There, the North Atlantic Council — consisting of ambassadors and permanent representatives of member nations — makes all political decisions. Defence ministers or heads of state may represent their nations depending on the importance of the issue at hand. Decisions are made only on the basis of a full consensus.

A military committee advises the council, the Defence Planning Committee and Nuclear Planning Group on military issues. The committee consists of military representatives from the member states. It is NATO's senior military authority.

The committee's chair is considered to be the organization's chief military adviser. Canadians have held the post three times:

1952-1953 Lt.-Gen. Charles Foulkes.

1980-1983 Admiral Robert H. Falls left the post in a storm of controversy in 1983 after saying he thought it would be unnecessary to deploy Pershing missiles in Europe in response to Soviet threats to deploy SS-20s.

2004 Gen. Ray Henault, Canada's chief of defence staff .

NATO military forces are composed of forces made available by the member states.

NATO Milestones:

April 4, 1949 The Treaty of Washington (North Atlantic Treaty) is signed by 12 nations. U.S. Gen. Dwight D. Eisenhower is appointed the first supreme allied commander, Europe.

1954 Soviet Union suggests it should join NATO to preserve peace in Europe. U.S. and U.K. reject this, seeing it as an attempt to curtail the buildup of NATO forces in Europe.

1955 After objecting to Germany's admission into NATO, the Soviet Union joins Albania, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland and Romania in forming the Warsaw Pact.

1962 At the height of nuclear brinkmanship between the U.S. and the U.S.S.R., U.S. President John F. Kennedy agrees to dedicate part of his nuclear arsenal to NATO.

1963 NATO stages Operation Big Lift, which sees 14,500 troops flown from the U.S. to West Germany in a display of NATO's quick reinforcement abilities.

1966 NATO announces it will reserve the right to use nuclear force if necessary to defend its member nations. This same year, France withdraws its military — but not its diplomats — from the organization.

March 1970 NATO launches its first communications satellite from Cape Kennedy. The satellite is to be used for better defence co-ordination and nuclear planning.

February 1987 NATO and Warsaw Pact enter formal talks aimed at reducing the number of conventional forces in Europe.

July 1990 Less than one year after the Soviet Union loosened its grip on its East European satellites and allowed liberalization, NATO issues its London Declaration on the End of the Cold War. This signals a new beginning for both NATO and the Warsaw Pact group of nations. Also this year, East and West Germany unite, bringing the former East into NATO.

1995 Under UN mandate, NATO enforces the Bosnian peace agreement.

1999 NATO conducts 11 weeks of bombing raids on Yugoslavia. It is the first time NATO acts against a state without UN approval.

November 2002 NATO leaders approve plans to set up a rapid response unit that could be deployed to deal with terrorist threats, natural or man-made disasters, or to be the first wave of a much larger NATO response in the early stages of a crisis.

Jan. 1, 2004 Dutch Foreign Minister Jaap De Hoop Scheffer becomes NATO secretary general, succeeding Britain's Lord Robertson.

Membership expands to 26 nations as former Eastern Bloc countries Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia join the alliance.

Oct. 13, 2004 NATO announces its Response Force has reached "initial operational capability" and is ready to act whenever and wherever needed. The force — composed of elite land, sea and air troops — was set up mainly to counter terrorist threats.

Nov. 17, 2004 Canada's chief of defence staff, Gen. Raymond Roland Joseph Henault, is named chairman of NATO's military committee, becoming the organization's chief military adviser. He succeeds Gen. Harald Kujat, a German who held the post since 2002.

Nov. 29, 2006 NATO reinforces commitment to securing Afghanistan with member nations promising to send more troops to strengthen the 32,000-strong NATO contingent. NATO also announces a new rapid-reaction force of 25,000 is ready to be called upon in the event of terror threats, failed states or regional conflicts.

Aug. 19, 2008 NATO suspends relations with Russia, saying it will not hold meetings with the country until it withdraws its troops from Georgia. In December 2008, diplomatic contact resumed. "We signalled our unhappiness with Russia using military force to invade Georgia [and] change borders by force of arms," Kurt Volker, U.S. ambassador to NATO, said in a statement. "Yet we also signalled a desire for a co-operative relationship with Russia."

April 2009 On the 60th anniversary of NATO, 28 world leaders meet in Strasbourg France. On the first day of the meetings U.S. President Barack Obama calls for a more focused commitment in Afghanistan. Croatia and Albania become members of NATO.