This is a spinoff of Dave Howery's "Vietnam invades Thailand" thread.
I don't see a large-scale Thai-Vietnamese conflict coming from the POD he proposes (Cambodian rebels, et al.) But I can imagine a Thai-Vietnamese conflict starting with an earlier POD.
It's this: OTL, Pol Pot was insanely aggressive towards Vietnam and merely obnoxious towards Thailand. TTL, let's reverse these, and have Pol Pot direct his madness towards the feudal-capitalist running dogs in Bangkok.
I think this is a stretch -- there were underlying nationalistic and ideological currents pushing the Khmers Rouges towards a confrontation with Hanoi -- but let's handwave [handwave] and say Pol Pot just happens to be daft in this particular way.
Now what?
Well, I think the Thais would be slow to invade -- slower than the Vietnamese OTL. We're probably talking '80 or '81. So, many more Cambodian dead, alas.
And they'd look for a non-Communist Cambodian resistance movement (probably Son Sann) to be the tip of the spear. Well, so did the Vietnamese OTL! But the Vietnamese then insisted -- in the face of overwhelming evidence to the contrary -- that they weren't fighting in Cambodia. Really: they said they were just providing logistical support to Heng Samrin and the other anti KR (really mostly former-KR-turned-anti-KR) Cambodians. Which was so obviously nonsense that it helped turn world opinion well against them.
The Thais, I think, would try to make this a /bit/ more real. So they'd likely spend a year or two building up Son Senn, and maybe grabbing a foothold in western Cambodia.
That done, can SS + the Royal Thai Army go all the way to Phnom Penh?
Probably. Pol Pot had gutted his army. Think Stalin's purges, but five times worse. And also, the KR had little armor or heavy artillery to begin with, and most of what they did have had broken down by ''78 from lack of parts and maintenance.
Worse and worse, formal KR doctrine was a weird mishmash of Maoism and triumph-of-the-will. Basically, they downplayed the importance of things like armor and airpower in favor of the almighty guerrilla. After all, the US had unleashed fantastic airpower against them, and Lon Nol had had armor, and they'd still lost the war. Right?
So, yeah: any halfway decent army could take them out. But the Thais were a weaker force than the Vietnamese, and not configured for a large-scale offensive campaign. So it would probably take them months instead of six weeks.
Meanwhile, what's Hanoi doing? Well, it's unlikely that Pol Pot will have played nice with the Vietnamese. If we flip his OTL attitudes towards Vietnam and Thailand, then he's been plenty obnoxious enough. So the Vietnamese probably won't intervene to save him.
But they still won't be too happy to see a neighboring Communist regime overrun by feudalists and counterrevolutionaries. So upon consideration, I think that what happens is, once the Thais are clearly winning, the Vietnamese invade anyway. Glance at a map and you'll see that Phnom Penh is much closer to the Vietnamese border than to the Thai side. So, Hanoi can let the Thais fight their way halfway across the country, and then intervene with a knockout blow. Think Poland in '39, kind of thing.
Now a key question becomes, is there a plausible Communist alternative to Pol Pot? OTL there was, because he'd purged the Eastern Zone cadres in advance of war with Vietnam, and some escaped the purges. If that hasn't happened, then maybe the Vietnamese don't have a puppet.
But, hell, they'll come up with someone; Communist regimes were creative that way. So they invade and install *Commie in Phnom Penh. They may first try reasoning with Pol Pot, but that's not likely to work so well. So they may break new ground in socialist brotherhood by taking the son of a bitch out, popping a cap in his evil, torturing, genocidal ass, and then reporting that Comrade Pol died valiantly at the head of his troops after bequeathing leadership of the Revolution to his dear Viet brothers in arms. Or some such.
But now the Vietnamese and Thai forces are bumping into each other in the middle of Cambodia...
Thoughts?
Doug M.