From this interesting story on theatlantic.com:
Before Vietnam became synonymous to 1970s Americans with a seemingly endless war, it might have conjured images of French wines and big game hunting. In the early 1960s, the U.S. government tried to encourage tourism in Vietnam in elsewhere in Southeast Asia as a sort of travel diplomacy. "Tourism's proper development, it was believed, could serve important U.S. geostrategic objectives," writes University of Minnesota history professor Scott Laderman in his 2009 book Tours of Vietnam: War, Travel Guides, and Memory. Friendly American faces could soften the reputation of the U.S. overseas, it was thought, and their souvenir purchases might bolster emerging economies.