Mid-Atlantic, and why is West Virginia in the Mid-Atlantic? It belongs in either the South or Midwest.
I mulled over both those options, but in the end decided that the 'Mid-Atlantic' was the best compromise solution. Considering that West Virginia seceded from Virginia in part because of the latter's decision to join the Confederacy, combined with the fact that there were few -if any- slaves or slaveholders in the state ruled out the South for me.
And as for the Midwest, I came very close to including West Virginia with that region, but decided against it in part because of the fact that West Virginia has more in common with Pennsylvania than, say, Ohio, given its long and intertwined history with coal-production.