The Cold War in South East Asia was not only a confrontation among big powers, but also a struggle among South East Asians themselves. Vietnam’s occupation of Cambodia (December 1978-September 1989), especially, marked a critical episode in the history of South East Asia during which the three Indochinese states and the six South East Asian states of the Association of South East Asian Nations (ASEAN) polarized, thereby constituting a source of instability that lasted for more than a decade. However, the conflict was viewed as a challenge to the latter six states, and one that could not be ignored. In part, this was because of the Treaty of Amity and Cooperation in South East Asia, ratified in February 1976, which laid the basis for a regional order of peaceful coexistence. As a sub-regional organization, ASEAN had come to strengthen its collective will in order to resist diplomatically Hanoi’s intention of undermining the rationale of the only such entity in Asia. For by then, ASEAN had established certain rules and norms in the conduct of its external relations and among member countries. Concomitantly, by tying the hands of the Vietnamese, the ASEAN states could use the Cambodian conflict as an interlude within which to accelerate their own economic development, based on an export-oriented industrialization.