He hinges his post on the statement that “Pro-Soviet regimes took over not only South Vietnam, but Laos, Cambodia, and Burma.”
Laos and Cambodia were both destabilized as a result of the lengthy Vietnam War.
Both American and Vietnamese forces entered landlocked Laos. It was ripe for picking off by the Chinese or the Vietnamese by the time the war in Vietnam ended. The Vietnamese nationalists had sponsored the Pathet Lao against the French colonial occupation since the 1950s.
Cambodia was so brutalized by its fate in the war that its monarchy fell to the Khmer Rouge, who were Chinese-influenced. The Vietnamese were able to extend their influence into that country by invading and installing their own regime.
Even after the devastation of forty years of war, Vietnam’s population was several times larger than Cambodia or Laos combined, something that made it easier for them to dominate the other countries.
Myanmar/Burma was ruled from 1962 by a military dictator. He didn’t leave power until 1988. Myanmar is still under military rule.
So what are we left with for the Southeast Asian domino theory? Two countries with small populations that neighbored Vietnam, were directly involved in the conflict, and whose governments were in disarray because of their involvement with the war, were invaded by their more populous neighbor. The third country in the example was ruled by the same person for 13 years before and 13 years after the fall of Saigon, and his former subordinates still run the country.
When you base a theory on faulty information, the whole thing collapses like a house of cards. Or perhaps dominos.