Not about Vietnam, no, we weren't involved in that one, but I've seen it plenty of times since. When it is being applied to a country it's just silly, because it is obvious to anyone that most people can't leave since they have no right-of-abode anywhere else in the world, but when it is used for a subdivision of a country it seems to be that it has more force because it is theoretically possible for the people to move elsewhere in the country. "Get out of Maine" could be backed up with action in a way that "get out of America" couldn't (except by a "final solution").

(And yes, I am British and live in Britain.)