European founding members

Total NATO members: 12

The original North America Treaty Organization, created as a bulwark against the Soviet Union and as a hedge against the revival of European nationalism,; it was rooted in the Western part of Europe and in North America. The 12 alliance members agreed that “an armed attack against one or more of them… shall be considered an attack against them all.” Eastern Europe had fallen under Soviet sway and there was concern that Moscow's influence would creep westward.

Near the end of the Cold War

Total NATO members: 16

In 1988, NATO had expanded somewhat, but remained weighted heavily toward Western Europe. Just four countries -- Greece, West Germany, Turkey and Spain -- were added over four decades. That’s because the lines between East and West had hardened, with the United States and the Soviet Union dominating their respective spheres of influence. The fall of the Berlin Wall in 1989 would dramatically reshape the map.

Eastern expansion

Total NATO members: 28

Since the breakup of the Soviet Union, NATO has pushed deep into what was once Moscow's domain. Twelve nations have joined the alliance in the past 15 years, bringing NATO to its current level of 28 members. All the recent additions have been from Central or Eastern Europe, and three of the newer members -- the Baltic nations of Lithuania, Estonia and Latvia -- had been part of the Soviet Union.

NOTE: Total includes the United States and Canada. SOURCE: NATO.