In the fist half of the twentieth century, the "country" was depopulated of marginal farmers and their support infrastructure. The fraction of the population on farms dropped from 60+% to less than 10%. Many farm houses were abandoned and either burned or collapsed. Whole towns disappeared. The reason people left the farm was not a depression exclusively in farming, but a great technological leap forward in productivity.
At one time, Detroit was necessary as a living/staging area for the multi-tens of thousands of people working in the auto industry. At that time, it was essential that production facilities be centralized and turned into huge assembly lines running twenty four hours a day. What happened in Detroit happened elsewhere for various industries as it was no longer so necessary to centralize the industries so much. The difference is that many other such cities have moved on and become centers of modern business in other areas. That didn't happen in Detroit, probably because the political Powers actively prevented it. Detroit might have become a center of computer production, or finances, or "high tech" or whatever, but the not-so-smart leaders of that city either didn't think that was important or actively prevented it from happening. After all, it's hard to extract graft in-advance from a company considering moving to an economically-depressed area.
The best "bail-out" for Detroit would be to go under water for a few months, and then be literally "bailed out" like New Orleans. Then, they could flatten the city with Caterpillars and start over on level ground with a small village on the Detroit River supported by Great Lakes shipping traffic. Over time, it might even grow into a major US city.