By Suzanne Kelly
Special to CNN Interactive

(CNN) -- Many of the countries seeking NATO membership are doing so for reasons of protection.

Among the NATO criteria, countries must have established democracies, good relations with their neighbors and effective armed forces under civilian control.

Some observers say the Balkan states are most in need of NATO membership because of the security guarantees that come with membership. Slovenia and Romania have expressed their desire for membership but have been delayed for the time being by NATO.

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Below are thumbnail sketches of some of the countries seeking NATO membership:

Bulgaria -- Has a democratic constitution and has made a state-led effort in recent years to develop in the areas of science and education. Because of Bulgaria's strategic position, NATO has sough permission to use its air space in pursuing airstrikes against Yugoslavia.

Latvia -- Latvia declared independence in 1991 after more than five decades of Soviet rule. Has a democratically elected parliament known as the Saeima. Latvians from various political movements are allowed to run for parliament.

Estonia -- A republic based on a system of civil law, with no judicial review of legislative acts. Hosts a unicameral parliament with several political parties. Declared independence after Soviets' 50-year rule.

Lithuania -- Occupied by the Soviet Union for 50 years, Lithuania proclaimed its restoration of statehood in 1990 and renewed diplomatic relations worldwide.

Romania -- A Latin outpost in Eastern Europe since Roman times, Romania was for much of the postwar period ruled by a totalitarian communist regime. The Communists held power until 1989, when a revolution toppled the country's leader, Nicolae Ceausescu. Romania adopted a new constitution in 1991 to become a multiparty republic. In 1994, Romania became the first Central European country to join NATO's Partnership for Peace program.