Short answers, pulled from the story.
SEATO was a collective defense organization created by the Southeast Asia Collective Defense Treaty, signed on the 8th of September 1954 in Manila. Its formal institution was established on the 19th of February 1955 in Bangkok, where it was also headquartered. Eight nations joined during its lifetime, and it was dissolved on the 30th of June 1977.
SEATO was created primarily to block further communist gains in Southeast Asia, as part of the broader American policy of anti-communist containment. Secretary of State John Foster Dulles is considered the primary force behind the organization. Vice President Richard Nixon had advocated for an Asian equivalent of NATO after a 1953 Asia trip, and NATO served as the direct model.
The eight SEATO members were Australia, France, New Zealand, Pakistan, the Philippines, Thailand, the United Kingdom, and the United States. Only the Philippines and Thailand were actually located in Southeast Asia. The U.S. Senate ratified the treaty by an 82-1 vote.
SEATO never deployed its military forces due to persistent internal disagreements among members. France and the United Kingdom blocked military action in Laos, and British and French opposition also prevented SEATO involvement in the Vietnam War. Unlike NATO, SEATO had no joint commands and no standing forces, and its response protocol for communist threats was vague.
SEATO's Secretary General Pote Sarasin founded the SEATO Graduate School of Engineering in Thailand in 1959, now known as the Asian Institute of Technology. SEATO also established a Cholera Research Laboratory in Dacca in the 1950s, which grew into the International Centre for Diarrhoeal Disease Research, Bangladesh, and became the world's leading cholera research facility.
SEATO was formally dissolved on the 30th of June 1977 during the Carter administration, after many members withdrew or lost interest. Pakistan left in 1973 following East Pakistan's secession as Bangladesh. France withdrew financial support in 1975 after South Vietnam fell. A final exercise was held on the 20th of February 1976 before the organization formally wound down.