NATO's enlargement is high on the agenda of the alliance's three-day summit in Bucharest, Romania beginning on Wednesday. Leaders are going to decide whether to invite Croatia, Albania and Macedonia to join NATO. The following is a brief history of NATO enlargement in the past 59 years.
NATO was founded in 1949 as a transatlantic collective defense alliance with 12 members -- Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the United States.
In the 1950s, it took in three new states -- Greece, Turkey and West Germany. Spain in 1982 was the last to join before the end of the Cold War.
NATO, founded to defend West Europe from possible aggression by the Soviet Union and its Warsaw Pact partners, theoretically lost its reason to exist further, after the collapse of the Soviet Union and the subsequent disintegration of the Warsaw Pact in the early 1990s.
However, the alliance chose to further enlarge itself, embracing former Warsaw Pact member states.
In 1999, the Czech Republic, Hungary and Poland were the first former Warsaw Pact countries to join the alliance.
The single largest enlargement took place in 2004 when seven countries were admitted -- Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia -- bringing the total membership to26.
Ukraine and Georgia have applied for NATO's membership action plan, a program that will prepare an aspirant country for membership. But NATO allies are still divided on this issue.