Geography and demography give Middle America a military advantage over the northeast and the left-coast. It has the breadbasket of the Midwest, the Mississippi River (the longest navigable river in the world), the industrial heartland, vast reserves of oil, natural gas, and coal, access to the Atlantic and Caribbean oceans, and people who know how to build, farm, hunt, and shoot. I also posit that it would not me a war between the states so much as a war between the rural and industrial areas against the mega city states of Chicago, the Northeast Corridor, and the coastal cities of Southern California. In those cities squat the billionaire class handing out government cheese to the squalid masses.
Those states also have "vast reserves of oil, natural gas, and coal, access to the Atlantic and Pacific oceans (there is no such thing as the "Caribbean" ocean.)
Remedy this analysis by carefully examining the red-blue map as you do further on. However, you're also somewhat mistaken on that point as well: The blue cancer doesn't just exist in Chicago, but runs a significant length down the Mississippi river. St. Louis is every bit as awful as Chicago, just for example.
It's urban vs. non-urban that matters.