FortsThe regular army of the United States moved westward across the continent with the expansion of the nation. American sovereignty had to be exerted over new territorial acquisitions, and settlers moving west called for protection against the Indians. The military presence in the West came largely in the form of small installations (variously called posts, forts, camps, cantonments, or barracks), which were built at strategic sites along the lines of communication or in areas of Indian disturbances.