It's one of those hackneyed theories that has a grain of truth in it, but nothing more. Yes, perhaps fear of being nuked drove some people from the cities, but what actually drove a lot more people from the cities was racism, plain and simple. See https://en.wikipedia.org/wiki/White_flight That, a lot more than fear of nuclear war, is what drove suburbanization, along with the rising spending power of the middle class that made a detached home in the suburbs and a car achievable on a single salary.