With nothing left for him in Arkansas he headed west to make a new life for himself in Peace Valley. In his pocket he had papers giving him legal rights to all the waterholes in and around the valley.
Once the ranchers realize he owns all those waterholes, his life won't be worth the paper he's carrying in his pocket.
But no one realizes what they've cornered until Duke makes his stand and there will be no peace in the valley until he's through.