“As Menzies saw it, the risk in American policy was not strategic overreach but isolationism, and what an American withdrawal from Asia in the face of defeat would mean for Australia and its neighbors. As a young man of military age during World War I, and as a youthful prime minister at the outbreak of World War II, he knew how painful it was for Britain and its dominions to be at war without America. The crucial step, it seemed, was to ensure American commitment: Once that was achieved, victory would be certain. Australia’s “forward defense” strategy after 1945 was to make small, but effective, military commitments in order to keep both Britain and the United States, which Menzies called “our great and powerful friends,” committed to Southeast Asia.
Australians had good reason to believe in the domino theory. Since 1945 Southeast Asia had been a caldron of conflicts created by the complex combination of decolonization, the Cold War and longstanding local rivalries. By 1964 the region seemed to be at a tipping point. Malaysia was facing a confrontation with Indonesia, where the world’s third-largest Communist party was exerting increasing influence. Although not a Communist, Indonesia’s President Sukarno had received arms from the Soviet Union and boasted of his close ideological ties with China, North Korea and North Vietnam.”
Source: What Was Australia Doing in Vietnam? – The New York Times