I imagine that the process of getting both of the nations to reconcile would be easier after the end of the cold war, but I would not want to assume. Did the ASEAN respond to the Vietnamese-Cambodian war as a unified group, as individual nations, or am I so off base I need to reconsider my question?
South-East Asian here.
ASEAN condemned Vietnam for invading Cambodia and so indirectly backed to Khmer Rouge.
In retrospect, not ASEAN's finest moment.
The two nations weren't ASEAN members back then, and by the time they joined ASEAN (Vietnam in 1995, Cambodia in 1999) the Cold War was over and it didn't really factor as a consideration.