Prehistoric people lived in the Nebraska region as long ago as perhaps 25,000 years. At the time of European exploration, Nebraska was inhabited by several tribes, some of which farmed while others hunted buffalo on the plains. As tribes were forced out of their homelands by the expansion of white settlements, other Indian tribes gradually moved into the area. The Spaniard Coronado visited what is now Kansas and claimed everything around, including Nebraska, for Spain in 1541. La Salle sailed down the Mississippi River in 1682 and claimed the valleys of the Mississippi and all its tributaries, a region that included Nebraska, for France in 1682. Neither the French nor the Spanish settled in Nebraska. The first white men to cross Nebraska were probably two French brothers, Pierre and Paul Mallet, in 1739. In 1762, the French gave Louisiana to Spain but French trappers remained in the area and Spain never created an effective adminsitration in Nebraska. The territory reverted to France in 1800 and was sold to the United States as part of the Louisiana Purchase in 1803. In 1812, Robert Stuart crossed the United States from west to east, establishing a course along the North Platte and Platte rivers that later became the Oregon Trail. In 1854, the territories of Nebraska and Kansas were created by the Kansas-Nebraska Act. The Homestead Act of 1862, which granted 160 acres of free land to frontier settlers, greatly boosted Nebraska's population. It was admitted to the Union in 1867 over the veto of President Jackson, who faced impeachment and feared that the state's new Republican senators would vote against him when he was tried by the Senate. In 1905, construction began on the North Platte Project, which provided irrigation to farmlands in western Nebraska and Wyoming. In many cases, the land turned out to be poor for agriculture and was bought back by cattlemen who returned it to grazing.