they recovered from population losses, regaining a total of 5,000 members by 1850. The Kansas–Nebraska Act resulted in numerous settlers arriving in Kansas; both abolitionists and pro-slavery groups were represented among those trying to establish residency in order to vote on whether the territory would have slavery. The Osage lands became overrun with European-American settlers. In 1855, the Osage suffered another epidemic of smallpox, because a generation had grown up without getting vaccinated. Subsequent U.S. treaties and laws through the 1860s further reduced the lands of the Osage in Kansas. During the years of the Civil War, they were buffeted by both sides, as they were located between Union forts in the North, and Confederate forces and allies to the South. While the Osage tried to stay neutral, both sides raided their territory, taking horses and food stores. They struggled simply to survive through famine and the war. During the war, many Caddoan and Creek refugees from Indian Territory came to Osage country in Kansas, which further strained their resources. Although the Osage favored the Union by a five to one ratio, they made a treaty with the Confederacy to try to buy some peace. Following the American Civil War and victory of the Union, the Drum Creek Treaty was passed by Congress on July 15, 1870, and ratified by the Osage at a meeting in Montgomery County, Kansas, on September 10, 1870. It provided that the remainder of Osage land in Kansas be sold, and the proceeds used to relocate the tribe to Indian Territory in the Cherokee Outlet. By delaying agreement with removal, the Osage benefited by a change in administration. They sold their lands to the "peace" administration of President Ulysses S. Grant, for which they received more money: $1.25 an acre rather than the 19 cents previously offered to them by the U.S. In 1867, Lt. Col. George Armstrong Custer chose Osage scouts in his campaign against Chief Black Kettle and his band of Cheyenne and Arapaho Indians in western Indian Territory. He knew the Osage for their scouting expertise, excellent terrain knowledge, and military prowess. Custer and his soldiers took Chief Black Kettle and his peaceful band by surprise in the early morning near the Washita River on November 27, 1868. They killed Chief Black Kettle, and the ambush resulted in additional deaths on both sides. This incident became known as the Battle of Washita