On June 19, 1965, Air Marshall Nguyen Cao Ky became Prime Minister of South Vietnam as head of a military junta, while General Nguyen Van Thieu became the figurehead chief of state. This arose after two years of severe political instability where South Vietnam experienced a series of leadership changes following a military-backed coup and assassination of President Ngo Dinh Diem in November 1963. Diem had served as Prime Minister in 1954-1955 and then as President from 1955 until his death in 1963. Following the coup, a junta was set up to lead the country, but which was racked by power struggles that led to a series of short-lived military governments.
With the formation of Ky-Thieu junta in June 1965, South Vietnam’s political climate stabilized somewhat.
In relation to the Vietnam War In May 1965, in a major effort to overthrow South Vietnam, Viet Cong and North Vietnamese forces launched attacks in three major areas: just south of the DMZ, in the Central Highlands, and in areas around Saigon. U.S. and South Vietnamese forces repulsed these attacks, with massive U.S. air firepower being particularly effective, and in mid-1965, Viet Cong and North Vietnamese forces retreated, and the danger to the Saigon government passed. By that time also, U.S. President Lyndon B. Johnson agreed to the U.S. military’s request and sent more troops to Vietnam, raising the total to 184,000 by the end of 1965. More crucially, he authorized U.S. forces to not merely defend U.S. facilities, but to undertake offensive combat missions, in line with American military doctrine to take the war to the enemy.
Meanwhile in June 1965, South Vietnam’s political climate eased considerably with the appointment of Nguyen Cao Ky as Prime Minister and Nguyen Van Thieu as (figurehead) Chief of State. The new South Vietnamese regime imposed censorship and restrictions on civil liberties because of the unstable security situation, as well as to curb widespread local civilian unrest. In 1966, Prime Minister Ky quelled a Buddhist uprising and brought some stability to the South Vietnamese military. Ky and Thieu were political rivals, and after Thieu was elected president in the 1967 presidential election, a power struggle developed between the two leaders, with President Thieu ultimately emerging victorious. By the late 1960s, Thieu had consolidated power and thereafter ruled with near autocratic powers. (Excerpts taken from Wars of the 20th Century: Volume 5- Twenty Wars in Asia.)