User blog comment:Spritydove/Deeper Thought into the Civil War/@comment-4692902-20120616075537/@comment-72.130.192.12-20120731050257

Here's a quote from the wikia on Forsworn. I think it sums up the difference between the Forsworn and Reachmen.

"The Western Reach region has historically been ridden with strife and turmoil; its location between High Rock and Skyrim, and its rich silver mines, has caused the two provinces to fight bitterly over its ownership. A peaceful agreement was reached centuries ago, but the intermingling of Bretons and Nords in the region has created a regionally distinct lineage of Bretons called Reachmen. Some among these formed the Forsworn, who have developed a unique culture of banditry, lawlessness, and hedge-magic, as well as a burning hatred for the Nords. They have been driven from their homes into exile. Some say they worship the Daedric Princes.

The Forsworn view The Reach as their ancestral land, and do not accept its Nordic occupation. They were briefly the rulers of Markarth until Ulfric Stormcloak and his men drove them out of the city about twenty years prior to the awakening of Dragons in Skyrim. They have since been a plague on the city, as well as on neighboring mines. In addition to their ancient gods, the Forsworn revere Hagravens, which can be found in several Forsworn encampments."