It's race, Landscape+Urbanism argues (after its sources), that was the undoing of Detroit. Far from there being a civic identity common to all Detroiters, it seems like racial identity--white, black--was the more noteworthy factor. Inasmuch as this led to the reproduction and intensification of inequalities, of which shortages of decent and affordable housing were key, this triggered a downwards spiral.
The focus on single-family houses led to perpetual housing shortages - particularly when combined with a history of official and unofficial policies that prevented blacks from obtaining housing. Unlike many of the eastern cities where the geography was a patchwork of ethnic enclaves, Detroit was much more literally black and white, as Segrue mentions, "class and race became more important that ethnicity as a guide to the city's residential geography." (p.22) While it was understood as a "City of Homes" for most, the influx of black workers from the South, who came in the 'Great Migration', were met with a consistent range of discrimination and violence, as existing residents perceived in-migration as a threat to their community, starting in the 1920s and continuing all the way through the 1970s.
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There were some inroads to employment in good jobs around WWII, driven by a tightening labor market, the coalitions of unions and civil rights groups, and some federal policies, which made sure that "blacks made significant gains in Detroit's industrial economy during the war." (p.27) There was still an undercurrent of racial tension, which played out in housing and employment, a continual topic that Segrue alludes to being a 'structural' racism that played out in Detroit, and were displayed in significant riots and other violence throughout the years, but that this didn't stop the influx of blacks coming into the city, leaving the Jim Crow south for something better. It's debatable if Detroit was much better.
The availability and quality of housing was poor for blacks - driven by a number of social and policy factors. While the New Deal had instilled a new ideology of opportunity for blacks - it had also instilled an ideology for current residents that the government would protect their property and the status quo. Thus the competing ideals of opportunity and protection played out in Detroit, and although, as seen previously, some gains were made - the majority of the wins came in maintenance of the status quo and protection from the new waves of poor, black residents.
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The geography of race was perpetuated by the real estate community as well, who were actively involved in the exclusion of blacks from housing. Another aspect was construction, with new houses rarely being built for blacks or in a price range that was suitable. As Segrue mentions, in "1951, on 1.15 percent of the new homes constructed in the metropolitan Detroit area were available to blacks." (p.43). Another major issue that shaped this geography in Detroit, and many other cities around the United States, was the concept of redlining. Maps were produced by the Federal Home Loan Bank Board, informed by local real estate brokers and lenders, to rate the neighborhoods in cities according to a scale from A (green) to D (red). While ostensibly a methodology for determining investment risk, the process became a de facto method for exclusion, disenfranchisement, and continued disinvestment in the minority areas.
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The promise of the New Deal, in post-WWII era, was predicated on government intervention to solve the problems of the city. One of those things was to provide adequate housing for the poor, whether this be true building of community and opportunity, or the more commonly wielded tool of 'social engineering' to make better citizens. Through a number of acts, the US developed policy and funding for many types of affordable housing, complementing the already robust subsidies of single family home construction and highway building.
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The problem in Detroit, was that nobody seemed to want public housing, as it was fought almost everywhere by both whites, unions, real estate agents, developers and even some established black residents. The adjacency of even some black areas was problematic, and developers had to make deals with the FHA, such as the 1 foot thick, 6 foot high wall that separated the new development from the old - remnants of which still exist. This sort of approach reinforced the FHA's official policy, not of true equality, but as mentioned by Segrue, even with some of the more enlightened bureaucrats, "a separate but equal philosophy." (p.67)
I'll be watching for the series as it's completed. If it turns out Detroit's only role now is as a negative role model, that may be enough.