The California Gold Rush of 1848 – 49 spurred western migration , the California Genocide and the creation of additional western states . After the American Civil War , new transcontinental railways made relocation easier for settlers , expanded internal trade and increased conflicts with Native Americans . Over a half-century , the loss of the American bison ( sometimes called " buffalo " ) was an existential blow to many Plains Indians culture . In 1869 , a new Peace Policy nominally promised to protect Native-Americans from abuses , avoid further war , and secure their eventual U.S. citizenship . Nonetheless , large-scale conflicts continued throughout the West into the 1900s
California Genocide
California Genocide
United States