Southeast Asia Treaty Organization
Flag of SEATO.svg
Type Intergovernmental military alliance
Headquarters Bangkok, Thailand
Region served Southeast Asia
Membership See Members
Official languages English, Thai, Filipino, Urdu, Mandarin Chinese, Cantonese, Portuguese, Bahasa Indonesia, Malay, French
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The Southeast Asia Treaty Organization (SEATO) is an international organization for collective defense in Southeast Asia created by the Southeast Asia Collective Defense Treaty, or Manila Pact, signed in September 1954 in Manila, Philippines. The formal institution of SEATO was established on 19 February 1955 at a meeting of treaty partners in Bangkok, Thailand. The organization's headquarters were also in Bangkok.



The organization was formed in 1954 in an objective similar to NATO in Europe. The objective was to contain the spread of communism in Asia after the formation of the People's Republic of China in 1949 as well as Soviet influence in the region. Despite the name, only the Philippines and Thailand are currently the members belonging to the Southeast Asian region. The United States, Australia, New Zealand, and the United Kingdom are members of this organization despite their distances away. This has further emphasized the U.S.' alliance with the Philippines (1951), Thailand (1954), and the ANZUS members. Pakistan, the only South Asian country to join, stated that it applied for membership due to the struggle with India.

Post-Great Nuclear War of 1962

The organization survived World War III as Bangkok, Thailand was not targeted by the Soviet Union. Manila, the capital of the Philippines, was nuked. However, it was largely forgotten after the war as member nations lost contact with each other. To make matters worse, when the Philippines invaded Sabah in 1971, Filipino troops had minor clashes with Commonwealth troops belonging from the UK, Australia, and New Zealand. These Commonwealth troops were stationed in the Federation of Malaya during the Indonesia-Malaysia confrontation when the Philippines took advantage of it to seize Sabah from Malaysian control. After the treaty of Port Moresby in 1974, all sides ceased hostility, although relations between the Philippines and Malaysia would be soured.

The idea of another form of collective defense occurred again when news of the Soviet Union invaded Manchuria and re-established the People's Republic of China in 1987, as well as news of a socialist government in Vietnam ruling since 1960s. Leaders from the regional countries met again in Bangkok and "re-established" the organization in 1988. Unlike the previous attempt, this time it would be similar to NATO wherein an attack on a member state would illicit the response of all members. SEATO is currently looking for more members to halt the flow of communism in Asia.


Original Member States (1954-1962)

Map of SEATO member countries - de

Member states as of 1959.

  • Flag of Australia Australia
  • Flag of France France
  • Flag of New Zealand New Zealand
  • Flag of Pakistan Pakistan
  • Flag of the Philippines (navy blue) Philippines
  • Flag of Thailand Thailand
  • Flag of the United Kingdom United Kingdom
  • Flag of the United States United States

1988 Re-establishment

  • Flag of Commonwealth of Australia and Newzealand Australia-New Zealand
  • Flag of France France
  • Flag of Pakistan Pakistan
  • Flag of the Philippines (navy blue) Philippines
  • Flag of Indonesia Indonesia
  • Flag of Thailand Thailand
  • Flag of Singapore Singapore
  • Flag of the Republic of China (1912-1928) United States of China
  • Jericho flag (TV series) United States of the Pacific

Observer Nations

  • Flag of the Republic of China Republic of China
  • Flag of the Pearl Delta Zhusanjiao


  • Flag of the Trust Territory of the Pacific Islands Trust Territory of the Pacific Islands (USP)
  • Flag of Australia ANZ Antarctic Territory
  • Flag of the Philippines (navy blue) Philippine-held Spratly Islands
  • Flag of Tibet Tibet