Ok this would only become open after the first war and the normal forsworn quest have been finished.
2 camps will appear. One out side of Mor Khazgurand and the other is on the Ysgramor's Tomb island
Story
After Some time the forsworn decided it was time to Take a front to retake their ancient home in skyrim. The victim they chose who was most even to their own were the orcs who only held 4 strongholds but were separated by a large amount of ground. The orcs who quickly learned of this have started recruiting orcs around the reach to help in this fight.
You can choose ether side.
You can join the orcs at the Mor Khazgurand camp simply talking to the general orc
to join the forsworn go to the Ysgramor's Tomb island camp and talk to ether Madanach or a Forsworn brave heart depending on how the 2 original forsworn quest turned out
By choosing the forsworn they will no longer be hostile towards you. You can also unlock the ability to become their king
By choosing the orcs you can enter strongholds if you wernt aloud to before and in the end you can become the grand war chief.
Thats all I have now
I had to leave to work but when Im back ill edit it some.