There are two very different sorts of Americans who venture abroad, as more than tourists or journalists, to so-called trouble spots. There are military people and “gold-mining” adventurers. And there are diplomats and teachers. In Vietnam, for instance, the US sent waves upon waves of troops and contractors to wage war for more than a decade in a military adventure that ended badly. A comparative trickle of Americans has gone to Vietnam since the war, often on their own initiative, to try to help undo the damage.