 Arkansas Territory, which included the present State of Arkansas plus most of the state of Oklahoma, was created out of the southern part of Missouri Territory in 1819.Originally the western border of Missouri was intended to extend due south to the Red River.However, during negotiations with the Choctaw in 1820, Andrew Jackson ceded more of Arkansas Territory to the Choctaw than he realized, resulting in a bend in the border between Arkansas and Oklahoma at Ft. Smith, Arkansas.