https://www.theatlantic.com/magazine/archive/2014/06/the-cas...
https://www.npr.org/2017/05/03/526655831/a-forgotten-history...
One article is about the south and the other one is about racist policies in the 30's. In the 30's there were essentially no people to be racist against in my community.
You're talking about urban planning departments, the concept is ludicrous in my home town which you could walk across in an hour surrounded by towns which you could walk across before finishing a sandwich.
It wasn't accidental in many smaller towns:
https://en.wikipedia.org/wiki/Sundown_town
I do expect that the Great Depression also contributed with small minority communities moving to cities.
The census count for "black" in my county in 1920 and 1900 was 5. Not 5%, 5. It was 99.97% white.
It's a fact that people seem to have quite some trouble with. Much of the midwest is nearly entirely white (and at that a pretty narrow subset of northern europeans) because only a small set of people had any interest in settling there.
The white population was "down" to 98.9%
I think the threat of race-based violence would have made this very difficult. One family, perhaps, but a little neighborhood? Not OK -- I'm thinking specifically about the Tulsa riots of 1921 and other racial violence (https://en.wikipedia.org/wiki/List_of_incidents_of_civil_unr...).
(Grew up in suburban Kansas and spent plenty of time hanging around towns like the fictional Gedanken.)
Iowa has a history of progressivism. For example in 1851 it was the second state to legalize interracial marriage. In 2009 it was the forth state to legalize same-sex marriage (and not through any change of the laws, the Iowa supreme court decided it was legal)
I know the culture I experienced was not pervasive in the whole midwest. I'm also not saying that there weren't bigots, but it was certainly very much different than a lot of other places in this country.