...so...suppose that for some reason (let's just butterfly out the reason for that) the mandated Vietnamese elections go forward as per usual. Perhaps Ho Chi Minh has a tummy ache and Vo Nguyen Giap doesn't live to see it.
So...the American government is still incredibly freaked out about Communism. Row of dominoes and all that. And in 1962, Sukarno begins the Konfrontasi against Western forces in Indonesia.
So the US decides that Indonesia is the next domino, after Korea and Vietnam, and begins turning it's strategic and tactical attentions towards Borneo. Britain, Australia, and New Zealand are waiting for them.