If explorers came from another planet and researched our human ways, this story would make no sense to them. A great and wealthy nation voluntarily chose to cease investing in the housing stock of much of their greatest cities, cutting off the flow of capital and credit to whole sections of their cities. When those sections declined, as they would as surely as a garden never watered, nor fertilized, nor re-seeded, adjacent sections of the city were also starved.
Eventually, an enormous amount of capital accumulated in urban land, houses and institutions was simply destroyed. To compensate for this destruction of wealth, this great and wealthy nation expanded into the farmlands surrounding the cities, investing in roads and automobiles, destroying the environment and the local food supply of their population.
(I read somewhere that greater metropolitan Chicago is about the same population it was at the end of WW2, but now takes up twice as much land.)
Romantic Capitalist Utopians (otherwise known as Libertarians) believe that operation of the free market will inevitably result in the most efficient use of capital. The market is ultimately rational, they think. Rand Paul recently ventured the opinion that segregation would have eventually gone away because it was bad business for a firm to repel paying customers and not hire the best workers. A hundred years of history refuted by an ophthalmologist's logic. There is also an argument that, given enough time, the slaveowners of the ante-bellum South would have seen the inefficiency of the slave economy and freed their slaves. They would have rather died, and many did.
It was illogical and irrational and tremendously inefficient and short-sighted for a great nation to stop investing in its great cities. Yet, the United States of America did just that. It did so because the imperatives of white nationalism were more compelling than the ideal logic of capitalism. (Under the simplistic ideal logic of capitalism, banks should have been rushing into the neighborhoods where African Americans were moving, eagerly competing for the chance to write the mortgages for the housing hungry migrants. Under that logic, people of all races in all neighborhoods would have sold their houses to the highest bidders, no matter their color.)
The emotional commitment to white nationalism is more powerful than the logic of the capitalist market. We have to remember that fact, because it means that it won't 'get better' on its own. It won't get better until we rethink all of our history and acknowledge that America was, in part, an African country from the time of the first settlements onward. We were never a white nation. We didn't become multicultural; we always were.