This timeline of the American Old West is a chronologically ordered list of events significant to the development of the American West as a region of the United States prior to 1912. The term "Old West" refers to a vast geographical area of imprecise boundaries, but is generally defined as lands west of the Mississippi River. The region was inhabited for millennia by various groups of Native Americans, and later served as a frontier to European powers, beginning with Spanish colonization in the 16th century. British, French, and Russian claims followed in the 18th and 19th centuries. After the American Revolution, the newly independent United States began securing its own frontier from the Appalachian Mountains westward for settlement and economic investment by American citizens. The long history of American expansion into these lands has played a central role in shaping American culture, iconography, and the modern national identity, and remains a popular topic for study by scholars and historians.