Southeast Asia Treaty Organization (SEATO) was an alliance of eight nations that signed the Southeast Asia Collective Defense Treaty in Manila, the Philippines, on Sept. 8, 1954. The members were Australia, Britain, France, New Zealand, Pakistan, the Philippines, Thailand, and the United States. Pakistan withdrew in 1972. SEATO was dissolved in 1977.
The treaty was initiated by the United States after Communist forces defeated France in Indochina (present-day Vietnam, Laos, and Cambodia). The United States claimed that the alliance was needed to prevent the expansion of Communist influence in Southeast Asia. Under the terms of the treaty, member states agreed to help defend one another–as well as other designated nations–against military aggression. This aggression included threats both from other nations and from forces within member nations.
SEATO did not become an effective alliance. It failed partly because many Asian states, including India, Indonesia, and Japan, did not join. Also, its members disagreed on the extent of the Communist threat and on how to meet it. Only Australia, New Zealand, and Thailand sent combat troops to support American intervention in the Vietnam War (1957-1975).
