White flight swelled the population of suburbs but they were already substantial. I think it would be a misleading picture if you just choose one point in a continuous process and start from there.

We don't need to create the universe to bake an apple pie from scratch. I agree that a history of the suburbs might begin before WWII, but the general concept of needing to start at the beginning is a slippery slope. I'd say nearly all histories must pick an arbitrary start, mid-stream.

In that case I recommend the commuter train, which created inner-ring suburbs which still exist. Not exactly ancient history anyway.