User blog comment:Thedoucheinthenorth/The Civil War - Why it is great/@comment-4692902-20121102005428/@comment-5135631-20121107221438

Quite right; they are similar ethnically and culturally, but the Forsworn are a militant group who represent Reachmen culture. Like the Empire or Thalmor might call Stormcloaks 'Nords' as a generalization.

On the issue of religion, Reachmen religion advocates human sacrifice and dark sorcery, you can understand why Nords don't want them to practice that shit.