America's Steam Empire
technicshistory.com
technicshistory.com
Coal was expensive and scarce (ish). So while railroads did build their infrastructure out of durable materials like stone, the gentle grades and wide turns were necessary to allow smaller, less powerful, more efficient locomotives to move freight around the nation.
In North America, that was not the case. Coal was cheap and plentiful, and available from all sorts of vendors and locations. Ultimately, it was easier to overpower obstacles with bigger locomotives than to put the effort into wringing maximum efficiency from what you had. The consequence was a much more rapid pace of technological development. And when the markets opened up in the UK, their firms were not prepared to compete.
I'd be very surprised if that didn't continue to be true. I saw one that asserted that the American middle class didn't emerge until the 1930s.
(The middle class was well established by the time of the American Revolution.)
It gets harder to define something with an answer more explanatory than "that thing is that thing".
You can see plenty of them in painting from before the Civil War and photographs afterwards.