system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is there such a large architectural diversity in Detroit?

Why are some parts so built up and others so run down? I read somewhere it used to be a booming city.
gpt
Detroit used to be the world's primary hub of automobile production with the big three US automakers (Ford, GM, and Chrysler) based there and building almost all of their cars there. In the first 2/3 of the 20th century this made Detroit a booming city, as you put it. 

In the 60's and 70's, foreign cars -- particularly Japanese -- became more popular because of cheaper car prices, comparable or better quality compared to US cars, and better gas mileage than US-made cars (which was super important during the oil crisis of the 70's). Because of the competition, it became difficult for the big three automakers to keep all their manufacturing in Detroit. All of their expenses -- particularly labor and real estate -- was expensive and they needed to figure out ways to produce cars more cheaply to compete with imports. So all of that manufacturing business from the Big Three began moving to other places in the US that had cheaper labor (and weaker labor unions) or moving out of the United States altogether. 

As Ford, GM, and Chrysler started moving manufacturing out of the Detroit area, that really decimated the area economically. 

Today, large swaths of Detroit and surrounding areas are abandoned like a ghost town because there is no longer the economy and jobs to support what was built there 50-100 years ago.