Which region did SEATO alliance operate in?

The Southeast Asia Treaty Organization (SEATO) was an international organization for collective defense in Southeast Asia created by the Southeast Asia Collective Defense Treaty, or Manila Pact, signed on 8 September 1954 in Manila, the Philippines. The treaty was drawn up both in English and French, whereas the Philippines was the depositary. Registered with the Secretariat of the UN on 13 April 1955, in accordance with the provisions of Article 102 of the Charter of the United Nations. Neither Poland nor Germany was its member.