Platte Purchase
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 3,149 square miles (8,156 km2) 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 time of the adoption of the Missouri Compromise. The area acquired was 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.
The region includes the following modern counties within its bounds: Andrew (435 square miles, 1127 km2), Atchison (545 square miles, 1412 km2), Buchanan (410 square miles, 1062 km2), Holt (462 square miles, 1197 km2), Nodaway (877 square miles, 2271 km2), and Platte (420 square miles, 1088 km2). It also includes the northwest suburbs of Kansas City, a small area of Kansas City proper, the cities of St. Joseph, Mound City and Maryville, Missouri, as well as Kansas City International Airport and almost all of Missouri's portion of Interstate 29, save the small portion which runs concurrently with Interstate 35 in Clay County.
...
Wikipedia