As the United States expanded westward in the 19th century, white settlers invariably clashed with Native Americans. Possessing entirely different concepts of land use and ownership, whites and Native Americans increasingly came into a conflict. Compounding the problem was the fact that the U.S. Army was the de facto authority in most parts of the American West at this time, especially after the Civil War, and often resolved issues through force. The United States had long regarded most Indian tribes as sovereign entities, with which it negotiated treaties in order to frame legal relations and resolve conflicts. In time, many Native American nations were settled on reservations that set them apart from the white settlers but that also relegated them to a separate and unequal existence. This map, created by the Office of Indian Affairs in 1923, shows the location of Indian reservations west of the Mississippi River. The names of the tribes are given and important geographic features such as state boundaries and rivers and railways are shown. Reservation schools and hospitals are also marked. In 1924, Congress passed the Indian Citizenship Act, which granted citizenship rights to Native Americans.