Why did Australia join the Vietnam war?

Answer 1

Since World War II, Australia had sought closer ties with the United States, as the USA held the same values with its own concerns about the spread of communism. Australia felt a degree of abandonment when Britain, its long-time ally, had to look to her own interests during WWII, and did not commit to helping defend Australia.

In 1951, Australia, New Zealand and the US signed the ANZUS Treaty which specifically pledged mutual aid, and aimed to discourage communist expansion while increasing the US presence and influence in the Southeast Asian region. It was in Australia's best interests to actively pursue a relationship with the US, so it was logical to support the US in its own support of the anti-communist South Vietnam. The SEATO Treaty of 1954 also pledged Australia to provide defensive action. Australia, too, was concerned about maintaining the South-east Asia region free of communism. The "Domino Theory" (the belief that if one country would fall to communism, then so would other countries) was a concern for Australia, as communism was starting to slowly spread southwards.

When Sir Robert Gordon Menzies was Australia's Prime Minister, he was extremely reluctant to involve Australia in Vietnam, and would not commit to the war. However, he resigned suddenly in January 1966 and nominated Treasurer Harold Holt as his successor. The new Australian Prime Minister Harold Holt immediately showed his unequivocal support of the USA in its fight against communism in Vietnam by uttering the unfortunate quote "All the way with LBJ". This cemented Australia's commitment to the Vietnam War.

Answer 2

They were members of the ANZUS Pact.