After WW2, where the occultists Hitler, Hiro Hito and Mussolini were defeated, but only after six million innocents were fed to the spawn of hell, the victors debated the best way to keep evil quelled. Unfortunately, and unknown to them, that vampire Truman betrayed mankind and argued for the continuation of colonial policies run mostly by corrupt followers of the netherlings. No more so than in Southeast Asia, where a patriot, the George Washington of his people and a former ally, Ho Chi Min, was forced to accept his former oppressors reclaim of power. Min had won the fight against evil and liberated the region, only to watch the minions of those dark hosts return to roost. There would be no peace.
At the siege of Dien Bien Phu, nuclear weapons had to be dropped to beat back the swarm of hatched lizardlings. The French withdrew, but the country of Viet Nam was split between human superpowers. The weapons of mass destruction brought an uneasy peace to global humanity but did not check the rise of new immortals hellbent on reclaiming their unrighteous place upon the surface. Viet Nam became ground zero for the evolving threat, Gargoyles and their greater cousins, Dragons.
An agreement was reached at a naval conference in the Gulf of Tonkin. A phony war would be started. An incident between navies was imagined. Jingoism would beat the drums for war against a phantom threat; down with insurgency and villainy. Escalate! Under that guise, special forces would be deployed among the militants to hunt down and slay demons with the full backing of all regional powers. Like many deals made and unmade, the pretend turned to the real as the lie was twisted and actual armed forces clashed after more and more foreign troops were deployed to the region. A smirking demon was said to have infiltrated every MEPS conning the lads to continue to fight the war their fathers had fought. A cold war turned hot, yet a mission remained. Destroy the last of these dragons before they can breed.
On one side you had the North Vietnamese, their partisan allies in the south the Viet Cong and PRG. Yet supporting them in armed conflict was Pathet Lao, Khmer Rouge, GRUNK, Chinese, the Soviet Union and North Korean armed belligerents. Most of these good men and true, patriots for their countries and cause. There only needed to be a few turncoats to vile inhuman forces to make the whole mucky muck a quagmire.
For the self-proclaimed good guys, there was the United States with South Vietnamese allies, the ARVN. Those troops were supplemented by the countries of South Korea, Australia, New Zealand, Laos, Cambodia, Khmer Republic, Thailand and the Philippines, The Japanese would have helped too, but they were bounded by treaty not to marshal armies for foreign battles.
How could this whole thing go so wrong? In a later generation the demons would be fought covertly or with cyber craft. But here in Southeast Asia the player characters are fighting the supernatural, while dodging the small arms actions of a tragic distracting ideological war. Not since Kipling wrote about the battles against the bloody Afghan goblins had such a situation unfolded. And you were there.