American cities weren't built for the car; they were bulldozed for the car. See Cincinnati, pictured below:

Further, we only have suburban sprawl because of government mandates. For example, thanks to restrictive zoning, it is literally illegal to build anything but detached single-family houses on the vast majority of urban land in this country.

Then there's the matter of parking minimums, based in arbitrary pseudoscience, that have resulted in the demolition of our urban cores.

And also the matter that most cities in America had incredibly extensive streetcar networks, before they were literally torn up. It's no accident that the city in the world with the largest tram network -- Melbourne, Australia -- is also the only city that left its historic streetcar intact.

The beautiful thing about fixing all this malarkey is we don't have to demolish and displace millions of people from their homes like we already did once only ~60 years ago. We just have to abolish those restrictive, Euclidean zoning laws and parking minimums and setback requirements and so forth. Let the invisible hand of the free market provide us with the density and walkability and transit-oriented development it's trying to provide us with!

The primary thing that needs demolishing is parking lots, and absolutely no one will miss those, I guarantee it.