ABSTRACT
The Third Indochina Conflict (1978-91) posed an immense political challenge for the ASEAN states. Vietnam’s invasion and occupation of Cambodia was a blatant case of aggression that altered the strategic environment in mainland Southeast Asia. This matter became the centre of ASEAN’s activities for a period of twelve years. One may wonder why the Cambodian question was such an important issue for the Association. No comparable apprehension had been demonstrated with Indonesia’s invasion of East Timor in 1975 or during the mid-1970s when Malaysia challenged Brunei’s international legitimacy. In contrast to these cases, a member state, namely Thailand, faced an unprecedented direct external threat to its national security as indicated by the presence of Vietnamese military troops on its border and repeated incursions into its territory.
