The first Americans believed to have reached the summit were a party led by General George Armstrong Custer in 1874, during the Black Hills expedition. The federal government took back the Black Hills and another strip of land in a new treaty in 1877. More than a decade later, it broke up the Great Sioux Reservation in 1889 into five smaller reservations, the same year that North Dakota and South Dakota were admitted as states to the Union. The government made some nine million acres of former Lakota land available for purchase for ranching and homesteading. Most American settlement in West River did not start until the early 20th century. The area attracted many European immigrants as well as migrants from the East.