Complex sentence: During the Steven's Treaty era, Washington Territory Governor Isaac Stevens called the Salish, Pend d’Oreilles, and Ksanka Band of Kootenai together in 1855 to negotiate the Hellgate Treaty with the U.S. Government establishing a reservation and a peaceful confederation of these tribes.
Split into simpler sentences: During the Steven's Treaty era, Washington Territory Governor Isaac Stevens called the Salish, Pend d’Oreilles, and Ksanka Band of Kootenai together in 1855 to negotiate the Hellgate Treaty. This treaty with the U.S. Government established a reservation and a peaceful confederation of these tribes.