All the way with LBJ
The Vietnam War, in essence a conflict between North Vietnam and South Vietnam, had wider implications because of North Vietnam's communist associations. In the wake of the Second World War, with Russia ascendant in Eastern Europe and China dominant in north Asia, western fears of a communist expansion throughout Asia were running high. The United States was concerned that, should North Vietnam prevail and turn Vietnam into a communist state, neighbouring countries such as Laos, Cambodia and Thailand were also likely to succumb in what was called the 'domino effect'. As an ally of the United States and with its own interest in seeing the South-East Asian region free of communism, Australia was an enthusiastic supporter of American policy in Vietnam.
America's fear of a North Vietnamese victory and its implications for regional politics led to its involvement in the war in Vietnam as an ally and supporter of the anti-communist South Vietnamese regime. Australia quickly followed suit, offering military trainers to assist South Vietnamese forces in a move aimed at supporting United States policy and addressing Australia's own regional concerns.
Over the following years both the United States and Australia increased their commitment to South Vietnam, including the use of conscripts in combat. Military might was not, however, sufficient to prevail over either southern communist insurgents nor the North Vietnamese Army. Even when United States and South Vietnamese forces did inflict a major battlefield defeat on their enemies during the 1968 Tet offensive, popular opinion in the United States and Australia turned against the war. The propaganda victory won by the communist forces ultimately proved to be of greater moment than their military defeat. After 1968 the United States began withdrawing its forces from Vietnam until, by late 1972, carriage of the war had been placed in the hands of South Vietnam which, in 1975, was defeated by the North.