US migration to the suburbs in the 1900s occurred in 2 separate phases. Before the onset of the atomic age, the growth was mostly organic. Advances in technology allowed people to buy cars affordably and refrigeration allowed food to be brought from longer distances so farms needn't be as close to the city. Thus land was cheaper. Post the onset, the organic growth was augmented with a push from gov't incentives. Growth was accelerated to the suburbs because of the urgent need/fear of nuclear devastation from a Soviet nuclear attack. Suburban growth would probably have continued at more natural growth rates rather to the extent and speed that was witnessed during the post-war boom years, if not for such a threat to populations and gov't continuity.
The basis is the size of the blast from a nuclear detonation. Such a blast is big enough to consider it's vertical effects. The more of your population that resides in a small square radius in tall buildings, the more vulnerable it is. Spreading them out along a 2-dimensional plane with shorter buildings increases their chances of survival. In the US, workers were moved out of compact neighborhoods of 6-story tenement buildings into 1 or 2 story houses on land previously held by farmers, wilderness, or large estates.
Most people don't know this angle because the survivability/continuity angle was not publicized. To avoid a panicky reaction, other spins were asserted. Marketing was done to promote the idyllic lifestyle of the suburbs; control of one's own house & land, having an automobile, freedom to go on trips with the interstate highway system, etc.
A sanity check is the comparison with WW1 soldiers coming back from Europe. Their experience lack the prominence of suburban migration that WW2 servicemen underwent. Surely, WW1 veterans also came back with familial aspirations as well. Coincidentally as well, America's investment in rail infrastructure started to diverge at this point in history as well. Rail is not conducive to post-apocalyptic travel. The tracks limit freedom of movement and require a high level of coordination most likely not available during emergency times.
One of the neat concepts that came with suburbia was the ownership construct. Ownership essentially means the removal of a private third party (to which a tenant pays rent) from their domicile context. So, an individual only retains a relationship with the gov't as a stakehoulder (via registration of property at the county clerks). What is interesting is why a system of renting suburbian houses didn't get implemented. It could be that ownership creates pride in one's houseowner and motivates the owner to invest energy in house maintenance. These skillsets come in handy during emergencies over renters which may rely on a building supervisor that may *not be present during a nuclear attack. Without a DIY know-how, that leaky-roof may *not be fixed and the inhabitants may get impacted and not survive as well. So from this perspective, this was a good thing that came out of the Cold War: the expansion of the middle-class.
Bringing us to today, there seems to be a reverse migration of the affluent from the suburbs into the inner cities. There's a renewed focus on urban renewal. I'm *not saying it's a result of migitation of nuclear risks from a series of strategic arms disarmaments; but there is a coincidence so one can wonder. Conversely, those left behind in the suburban thrive years before now have a chance to enjoy the fruits of owning a house as inner city families now appear to be migrating outward. It can be a new promise. It's up to one to see how to view it.