American Nations: A History of the Eleven Rival Regional Cultures of North America by Colin Woodard
Less than half way through. Eye opening. The character of our nation (and the nations of Mexico and Canada) is deceptively simple, if you only look at state lines and stereotypical regions. Of course, this coming from someone that did not know that his dad grew up in Appalachia (I thought southeastern Ohio had character enough).
So far, I identify the most the "Greater Appalachia," which I happen to live in.
I've read - a couple times - The Nine Nations of North America by Joel Garreau. It was a great read, but it was a snapshot of the area set - by default - in the late 1970s. Colin Woodard was right that the historical context of these "nations" is so informative, and that is what makes (so far) American Nations so compelling.