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. This expansion of the slave state of Missouri was in violation of the Missouri Compromise of 1820, which prohibited the extension of slavery in the former Louisiana Territory north of the parallel 36°30' north except within the boundaries of the state of Missouri as defined at the adoption of the Missouri Compromise. The area acquired is almost as large as the states of Delaware and Rhode Island combined, and extended Missouri north and westward along the river. St. Joseph, one of the main ports of departure for the westward migration of American pioneers, was located in the new acquisition.