I remember in the first year of my undergraduate degree, putting my hand up in my international studies class on the Vietnam War, supposing I was going to blow my tutor away with my 'hot take' on how it could be suggested that the domino theory was true. As you said, Indochina fell to communism 'one by one', how was this anything but a confirmation of the theory articulated in some way or another as early as 1950.

My tutor was uninterested. Particularly in reference to Cambodia, which was a growing interest of mine at the time, and the perfect example (I presumed) to get me a pat on the back for saying something interesting.

That was more than ten years ago, and I had always kept a little pocket of memory for both the embarrassment I felt at being rebuffed for something I thought was clever, but also because it really looks like domino theory was right.

I've noticed that you have submitted this question before but I neglected to answer it. This is for a couple of reasons, the first being the way you've asked it is actually kind of hard to answer. There are a lot of foreign policy experts, and all of the ones working in the 1970's would have had a lot to say on the topic. Hard to also place that against the larger 'story' of academia and trace this one particular notion and its treatment. There probably is an answer there, somewhere, but it would require a lot of reading and digging to find it.

So, having done, 'a little bit' of reading and digging. I'll start my answer with a quote that starts off this broader question you are asking.

‘The lessons derived by Americans reveal no fundamental consensus. Supporters of the (Vietnam) war concluded that one should avoid graduated escalation, that the soviet union was expansionist, that the ‘domino theory’ was valid, and that one must honour alliance commitments. Critics inferred that one should avoid involvement in national liberation wars, that the press was more likely to tell the truth about foreign policy than the administration, that one should avoid excessive reliance on military advice, that third-world revolutions are nationalistic, and that the United States should scale down its world role’ – Zimmerman and Axelrod, ‘The “Lessons” of Vietnam and Soviet Foreign Policy’, World Politics Quarterly Vol 34. No 1. 1981

So that goes someway in explaining the variance of opinion on the matter at the time. It also highlights the schism of opinion that many historians and experts had that was more or less based on their politics. But, as you said, at least some experts viewed these communist victories under the guise of the domino theory being proved correct. Some did not, and pointed to the nationalistic side of these conflicts. They also highlight, as you've mentioned, the role of the US itself in prolonging, exacerbating or creating the tensions between belligerents in these wars.

Now, in all those ten years since suggesting to my class and my tutor that the domino theory could be seen as correct, I have kept studying the field of Cambodia in particular. The basis for my 'hot take'. And I have come around to the vague dismissal of my suggestion that my tutor explained. This is where it becomes a bit complicated, as well as meandering slightly away from the 'academic consensus' that your question is about, but I think it is handy as it may explain why the theory itself doesn't carry much cache anymore. That being said I think from certain angles you can still make a case for it.

So I think the domino theory, itself a 'variant' of the containment theory, worked as a very simple rationale for going to war in Vietnam. This was a conflict policy experts in the US suggested was crucial for the global struggle against the spread of communism. However, its simplicity is reflected in its lack of nuance and understanding of the people and politics of the region and what will be the evolving relationship between the two communist superpowers.

So the formation of the Indochinese Communist Party in the early 1930s was headed by Ho Chi Minh, but under the auspices of the Soviets. Later, in the early 1950s, the party was dissolved into constituents based on each country, Cambodia, Laos and Vietnam. However all three parties were basically still staffed and under the control of, the Vietnamese. But this dynamic evolves as well, and in the subsequent 20-25 years, and toward the period of US exit from the region, is where we can look at whether the domino theory holds up or not.

At its most simplistic reading, then yes, look... more red parts of the map now, therefore domino theory. But what if some of those dominos were different colours? What if Vietnamese communists had little control over the Cambodian ones? What if China was pushing over one domino while the Soviet Union another? The factions here, more or less divided by the Sino-Soviet split, are a blow to the idea that the dominos simply fell one by one. But you could still make the case that it was 'communists' who were in charge now, regardless of their affiliation. But then again the outbreak of the Third Indochina War goes some way in challenging that notion that this was some concerted external communist effort to conquer the region.

This dovetails with the outlook provided in that foreign policy journal in 1981. It really depends on how you look at it, how deep you want to dig to prove or disprove a rather simple idea such as 'containment' or 'domino theory'. Were the rise of communist parties in Vietnam, Laos and Cambodia part of a scheme concocted by foreign powers, or were they indigenous movements that were more anti-colonial or nationalistic, led by communists with differing ambitions from their primary benefactors? Or is the outcome all that matters - the map before and after?

I guess I could boil that down to domino theory holds if you are only asking a very limited question. It should also be pointed out that the dominos didn't keep falling... but it must be acknowledged how shallow that reading of the situation is. It loses its value as a tool for studying the period because it lacks details to how this process is working. As a 'theory' (which is a stretch to think of it as) it lacks explanatory power, particularly when you look at what actually happened in these territories formally known as Indochina. If you asked a question like 'why did Cambodia descend into a civil war and then eventually succumb to the rule of the Communist Party of Kampuchea?' Just answering, 'the domino theory', doesn't really get you too far into the history of Cambodia... it is more a posture of US foreign policy analysts.