As the ASEAN member most vulnerable to a Vietnamese attack, Thailand was foremost among the ASEAN partners opposing Vietnam's 1978 invasion of Cambodia. Thailand's suspicion of Vietnamese long-term objectives and fear of Vietnamese support for an internal Thai communist insurgency movement led the Thai government to support United States objectives in South Vietnam during the Second Indochina War. In 1979, after Vietnam's military occupation of Cambodia had raised these same concerns again, Bangkok was compelled once again to ally with, an adversary of Vietnam and looked to Beijing for security assistance. In both instances, Thailand's actions hardened Hanoi's attitude toward Bangkok.
In 1973 a new civilian government in Thailand created a chance for some degree of reconciliation with Vietnam, when it proposed to remove United States military forces from Thai soil and adopt a more neutralist stance. The Vietnamese responded by sending a delegation to Bangkok, but talks broke down before any progress in improving relations could be made. Discussions resumed in August 1976. They resulted in a call for an exchange of ambassadors and for an opening of negotiations on trade and economic cooperation, but a military coup in October 1976 ushered in a new Thai government that was less sympathetic to the Vietnamese. Contact was resumed briefly in May 1977, when Vietnam, Thailand, and Laos held a conference to discuss resuming work on the Mekong Development Project, a major cooperative effort that had been halted by the Second Indochina War. Beginning in December 1978, however, the conflict in Cambodia dominated diplomatic exchanges, and seasonal Vietnamese military offensives that included incursions across the Thai border and numerous Thai casualties particularly strained the relationship.
Data as of December 1987