|When Britain and the United States settled on the 49th parallel as the boundary between the Canada and the US, the Nimiipuu homeland was first in Oregon Territory, and then Washington. President Franklin Pierce appointed Territorial Governor Isaac I. Stevens as the Indian agent to deal directly with Pacific Northwest tribes. The treaty process that Stevens brought to the Nimiipuu carried with it assumptions that are still relevant today. The Nimiipuu were treated as a sovereign governmental entity. They continue to be recognized by the US as such. Once a treaty is negotiated and ratified by the Senate, it has the force of law. The conditions of the Indian Treaties of the 19th century are still valid today.
At a treaty council held near Ft. Walla Walla on June 11 1855, the Nimiipuu with many neighboring tribes, agreed to set aside portions of their traditional homelands and cede the remaining lands to the federal government. The Nimiipuu ceded 5 million acres of land to the US, creating a reservation of approximately 8 million acres.