People keep talking about "Federalizing the National Guard" and now you've got other States pledging their NG to Texas in defiance of the Supreme Court (see image).
Compare the map you posted with the population map
There is many more people in the states that would be a Union Army, the fools that would wage war on the United States would be defeated and most Americans wouldn't even need to do anything but watch
The real problem is that they cut us up along crazy lines and lump the second and third groups together, so that the nice bluish-purple i see out my window looks bright red from space.