In 1541-1542 Spanish explorer Hernando de Soto and his party were the first Europeans to have entered Arkansas. In 1673 a group led by Jacques Marquette and Louis Jolliet traveled down the Mississippi River as far as the Arkansas River. In 1682 Robert Cavelier, sieur de la Salle, came down the Mississippi to its mouth. La Salle claimed the Mississippi Valley, including modern Arkansas, for Louis XIV of France and called it Louisiana. Henri de Tonti, one of la Salle's aides, in 1686 established Aux Ares, the community that later became Arkansas Post.
In 1762 France ceded to Spain Arkansas and its other possessions west of the Mississippi. The Spanish encouraged white settlement in the region. When the Spanish returned the region to France in 1800, fewer than 1,000 persons lived in Arkansas. Arkansas was part of the Louisiana Purchase of 1803. The area was part of the Louisiana District, the Louisiana Territory, and the Missouri Territory before being constituted as the Arkansas Territory in 1819. That territory also included Oklahoma.
Arkansas Post was the capital from 1819 to 1821, when Little Rock was made the capital. Arkansas settlement was slow until the 1820s, when the Chrokee and Choctaw Indians were removed from the territory. Arkansas had about 50,000 white residents in 1835, and on June 15 of the following year it entered the Union as the 25th state. Black slaves supplied most of the labor for the productive cotton plantations of eastern and southern Arkansas.