Why is he in Vietnam?: the nihlism of Dog Soldiers

Inevitably Robert Stone's Dog Soldiers (1974) recalls Graham Greene's The Quiet American - both about world-weary, desperate, drug-addled Anglo ex-pats in a a SE Asian country in the midst of or on the verge of war and insurrection. As I recalled, Quiet American concluded with a bombing scene in the capital city striking civilian targets - and Dog Soldiers begins that way, so maybe this is a sequel of a sort by another author. As noted yesterday, Stone is one of those writers I'd always meant to read who'd somehow slipped below my literary radar - and that's my bad; this novel gets off very well, establishes a mood and a voice right away, and feels very contemporary even though it's about 40 years old - could have been written today if you substitute the Vietnam War setting for just about any Third World civil war or insurrection. The protagonist, an American freelance journalist in Vietnam at the height of the war, named Converse, without any real drive or values, left wife (and child?) at home (California) in a pact of mutually agreed destruction, or so it seems - large part of the first chapter is his reading a letter from home, in which wife quite openly talks about her infidelities. Among the many strengths are Stone's facility with dialogue, his keen sense of detail to establish a setting unfamiliar to most readers (not sure how he gained his knowledge of wartime Vietnam - he didn't serve there, I'm quite sure), his pacing, and his stoner world view. Unlike Greene, he's not talking about a guy with lost ideals, corrupted by the war and by the Sybaritic ex-pat tropical culture - no, Converse has no values, he's not - so far as we know from the first few chapters - involved in espionage or service of any sort. He's trying to score a major drug deal, and his wife at home is part of the plot. Early on, he meets up with a far-gone (American?) woman who provides him with 3 k's of pure heroin - she has something going with the biggest and most corrupt drug manufacturer in Saigon - and he will get a cut if he can get it safely to his wife for distribution in the States. He has no moral qualms about this, and apparently no or little fear - he's just an entrepreneur, trying to make good. The novel is very promising, though one hopes, going in, that there will be some kind of character development or contrast - for first chapters, Converse seems hopelessly lost and all his acquaintances are equally nihilistic.