Related to boat people, related to the war, related to the political climate that led to it? What are you looking for? I ask because there's a blind spot and because the Vietnamese and Hmong friends I've had (A) don't like talking about it (B) are also disgruntled that no one has told their story. "How Vietnam happened" has best been explained by Barbara Tuchman's March of Folly. The dilemma it has, of course, is it's very much the American perspective, as with everything else related to Vietnam. The Vietnam War book most people refer to these days is Matterhorn, which is not non-fiction. I made it about halfway through; it's grim and deals far more with racism within the US military than it does with anything else. In that half there were no vietnamese at all. Superpower Interrupted is useful in that it's a non-American perspective, at least; it paints a portrait of Vietnam as a culture whose principle concern is not running afoul of China. For example, the region has historically been called Nam Viet but the Nguyen Dynasty renamed it Viet Nam to maintain peaceful relations with the Qings.