Nearly half a century later, after Fort Laramie had been built without permission on Lakota land. The Fort Laramie Treaty of 1851 was negotiated to protect travelers on the Oregon Trail. The Cheyenne and Lakota had previously attacked emigrant parties in a competition for resources, and also because some settlers had encroached on their lands. The Fort Laramie Treaty acknowledged Lakota sovereignty over the Great Plains in exchange for free passage on the Oregon Trail for "as long as the river flows and the eagle flies".