In December 1963 Sarit died in office. His deputy, Thanom, peacefully succeeded to the prime ministership and pursued without major modifications the foreign and domestic policies of his predecessor. Retaining the cabinet that he inherited from Sarit, Thanom focused his efforts on seeking to maintain political stability; promoting economic development, especially in security-sensitive areas; raising the standard of living; and safeguarding the country from the communist threat at home and abroad.

A notable departure from Sarit's policies, however, was the Thanom government's decision to shorten the timetable for the country's transition from the military-dominated leadership structure to a popularly elected government. The prime minister urged the Constituent Assembly, appointed in 1959, to finish drafting a constitution as soon as practicable. The new leadership also relaxed stringent official controls on the press, an attempt that the authorities said was aimed at creating a new, relatively liberalized, political climate.

Although the leaders agreed on the desirability of establishing what they described as a more democratic political system in tune with the country's heritage, there were indications that they disagreed on the pace of the projected change. Some leading officials thought that an early resumption of political activities would broaden the base of politics and strengthen popular identification with the government, the monarchy, and Buddhism. Others argued that the restoration of party politics at a time when the country was confronted with serious internal problems was likely to aid the communists in their efforts to infiltrate civic, labor, student, and political organizations.

The constitution was finally proclaimed in June 1968, but martial law, which had been imposed in 1958, remained in effect. Party politics were legalized and resumed shortly after mid-1968, and general elections for the new National Assembly were held in February 1969. Thanom's United Thai People's Party returned 75 members to the 219-seat lower house, giving them the largest representation of the 13 parties, while the second-running Democrat Party won 57 seats.

Thailand's annual economic growth rate in the 1960s and early 1970s averaged a booming 8 percent, much of it attributable to United States military expenditures there during the years of its involvement in Vietnam. An increased flow of foreign exchange resulted from United States and multilateral aid loans as well as from foreign investment, which came primarily from Japan, the United States, and Taiwan.

Foreign policy concerns focused on neighboring Laos, where it was believed a Pathet Lao victory would destabilize the North and Northeast and open Thailand to a direct attack by communist forces. Thailand allied itself closely with the United States position in the Republic of Vietnam (South Vietnam), permitting bases in Thailand to be used for raids on both the Democratic Republic of Vietnam (North Vietnam) and Cambodia. Although more than 45,000 United States troops and 500 combat aircraft were stationed in the country by 1968, their mission was not officially acknowledged for fear of possible communist retaliation against Thailand. Sarit also committed a division of Thai army troops to the war in South Vietnam.

President Lyndon B. Johnson's March 1968 announcement that the United States would halt bombing in North Vietnam and seek a negotiated settlement came as a blow to the Thai government, which had not been consulted on the change in policy. Although the defense of Thailand clearly remained essential to the security of Southeast Asia in United States strategic thinking, no provision was made for Laos, whose security the Thai saw as essential to their own defense.

While remaining loyal to its commitments, Thailand thereafter determined to restore flexibility to its foreign policy by moving away from one-sided dependence on the United States. The military, however, was anxious to continue Thailand's active involvement in South Vietnam and in Laos, where several thousand Thai "volunteers" were engaged against the Pathet Lao. Thanom urged United States backing for the Lon Nol regime in Cambodia in 1970 and proposed a formal alliance linking Thailand with Laos, Cambodia, and South Vietnam that would give the conflict in Southeast Asia the appearance of a war being fought by Asian anticommunists for Asian security. The plan failed to get United States support.

Communist activities in Laos and Malaya had already begun to affect the domestic situation in the South and the Northeast in the 1950s, and by the 1960s they presented a problem of increasing magnitude. Communist guerrillas, mostly ethnic Chinese, operated in jungle areas north of the Thai-Malayan border, where they had taken refuge from Commonwealth of Nations security forces during the 1948-60 Emergency in Malaya. A more serious threat in that same region were the Muslim insurgents of the Pattani National Liberation Front, a Thai separatist group composed of ethnic Malays. Meanwhile, in the northern provinces dissident Meo tribesmen reportedly had begun receiving training and arms from the Pathet Lao by 1950. In the Northeast, underground leftist parties took advantage of grievances over relatively poor economic and social conditions to rally opposition to the government. Faced with the problems in the South, North, and Northeast, the Bangkok government frequently identified regional unrest and protest against ethnic and economic policies with the genuine communist-based insurgencies that overlapped and often benefited from it. Opposition groups and critics of the regime in Bangkok were also generally labeled as communists.

Data as of September 1987