"The Best and the Brightest" by David Halberstam [View all]
It's been on my reading list for years, and I finally got around to it this summer.
It is a remarkably detailed account not only of the political environment in the late 40s/early 50s that created the environment that the USA would step in to after the French defeat (think yammering anti-communist Republicans), but also of the personalities involved in the decisions that led the country into committing to action in Viet Nam. These were well-accomplished people in business, government, and higher education who completely underestimated the resolve of the North Vietnamese to rid their country of foreign domination, and who also ignored the analysis of Asian experts and preferred the assessments of political operatives.
It's both enlightening and depressing to read how the country squandered a great opportunity to fully implement Great Society policies by wasting not only vast funds of money to a futile cause, but also sacrificing government credibility on policy and finances. The country has never recovered from the effects of that war.