>>2059971>The American small farmer died out during the farm crisis of the 80s and 90s, which explains the lack of density in American rural areas.This isn't the explanation.
First, lower density in the US isn't limited to rural areas. The cities themselves are far less dense than pretty much anywhere else in the world (especially East Asia). NY City is the only truly dense city in the US, and a few others are somewhat dense (Boston metro, San Francisco). Urbanists like to claim the US is "densifying" as they flood 3rd worlders into the country, waging soft war on China's behalf, but it's nothing like Asia.
Second, the effect you describe, while true, isn't large enough to really show up on that particular map. Relative to the rest of the world the US has ALWAYS been less dense.
The truth is that the US has just, historically, had an enormous amount of valuable and habitable land relative to its population size and technological power level. Americans had plenty of room to spread out everywhere east of the 100th meridian, where the Chinese (along with most of East Asia) did not, with substantial populations crammed into much smaller geographical areas. In 1850, there were some 400+ million people in China already, vs 20-25 million in the United States.
The most substantial migrations in the US in the last 100 years have been from the denser Northern cities and the "Rust Belt" into the south and "Sun Belt." Contrast Buffalo, NY with Phoenix, AZ. This was also coupled with growth of suburbs, so some cities proper may have seen stagnant or declining populations even as their metro areas as a whole were booming. Again this is due to the ease of expanding outward in most of the US. Places like Dallas, TX or Atlanta, GA aren't hemmed in by any major geographical features (mountains, oceans, deserts) and can grow in 360 degrees. It's usually easier, cheaper and more desired to build out rather than build up, and it's been that way for a very long time.