Nebraska is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwest; and Wyoming to the west. It is the only triply landlocked U.S. state. Indigenous peoples, including Omaha, Missouria, Ponca, Pawnee, Otoe, and various branches of the Lakota tribes, lived in the region for thousands of years before European exploration. The state is crossed by many historic trails, including that of the Lewis and Clark Expedition. Nebraska's area is just over 77,220 square miles with a population of over 1.9 million. Its capital is Lincoln, and its largest city is Omaha, which is on the Missouri River. Nebraska was admitted into the United States in 1867, two years after the end of the American Civil War.