Thorough examination of the antebellum fortifications that formed the backbone of U.S. military defense during the National Period The system of coastal defenses built by the federal government after the War of 1812 was more than a series of forts standing guard over a watery frontier. It was an integrated and comprehensive plan of national defense developed by the US Army Corps of Engineers, and it represented the nation's first peacetime defense policy. Known as the Third System since it replaced two earlier attempts, it included coastal fortifications but also denoted the values of the society that created it. The governing defense policy was one that combined permanent fortifications to defend seaports, a national militia system, and a small regular army. The Third System remained the defense paradigm in the United States from 1816 to 1861, when the onset of the Civil War changed the standard. In addition to providing the country with military security, the system also provided the context for the ongoing discussion in Congress over national defense through annual congressional debates on military funding.