Complex sentence: The Platte Purchase was a land acquisition in 1836 by the United States government from American Indian tribes all of which was east bank lands along the Missouri River that added to the northwest corner of the state of Missouri.
Split into simpler sentences: The Platte Purchase was a land acquisition in 1836 by the United States government from American Indian tribes. It comprised lands along the east bank of the Missouri River and added to the northwest corner of the state of Missouri.