During the first half of the 19th century, the U.S. government, responding to public pressure for land and resources, began concentrating Indian tribes on reservations. After the Civil War, growing numbers of settlers made survival on the Plains increasingly difficult for Native Americans, and resistance by many Plains Indians eventually led to open warfare. Several times during the summer of 1874, warriors left their reservations in present-day Oklahoma and moved north into western Kansas, where about 27 settlers were killed and many farms were destroyed. On August 24, 1874, a band of 25 Cheyennes led by Chief Medicine Water ambushed six men from a surveying company 11 miles southwest of here. The men fled while trading shots with the Cheyennes, but after three miles the oxen pulling their wagon were shot and all six men were killed. Two days later, their bodies were found and buried near a solitary cottonwood five miles south of here, and that lone tree gave the incident its name and remained a famous prairie landmark for many years.