The federal government owns roughly 640 million acres, about 28% of the 2.27 billion acres of land in the United States. Four agencies administer 608.9 million acres of this land: the Bureau of Land Management (BLM), Fish and Wildlife Service (FWS), and National Park Service (NPS) in the Department of the Interior (DOI), and the Forest Service (FS) in the Department of Agriculture. Most of these lands are in the West and Alaska. In addition, the Department of Defense administers 14.4 million acres in the United States consisting of military bases, training ranges, and more. Numerous other agencies administer the remaining federal acreage. The lands administered by the four land agencies are managed for many purposes, primarily related to preservation, recreation, and development of natural resources. Yet each of these agencies has distinct responsibilities. The BLM manages 247.3 million acres of public land and administers about 700 million acres of federal subsurface mineral estate throughout the nation. The BLM has a multiple-use, sustained-yield mandate that supports a variety of uses and programs, including energy development, recreation, grazing, wild horses and burros, and conservation. The FS manages 192.9 million acres also for multiple uses and sustained yields of various products and services, including timber harvesting, recreation, grazing, watershed protection, and fish and wildlife habitats. Most of the FS lands are designated national forests. Wildfire protection is increasingly important for both agencies. The FWS manages 89.1 million acres of the total, primarily to conserve and protect animals and plants. The National Wildlife Refuge System includes wildlife refuges, waterfowl production areas, and wildlife coordination units. The NPS manages 79.6 million acres in 401 diverse units to conserve lands and resources and make them available for public use. Activities that harvest or remove resources generally are prohibited. Federal land ownership is concentrated in the West. Specifically, 61.2% of Alaska is federally owned, as is 46.9% of the 11 coterminous western states. By contrast, the federal government owns 4.0% of lands in the other states. This western concentration has contributed to a higher degree of controversy over land ownership and use in that part of the country. Throughout America's history, federal land laws have reflected two visions: keeping some lands in federal ownership while disposing of others. From the earliest days, there has been conflict between these two visions. During the 19th century, many laws encouraged settlement of the West through federal land disposal. Mostly in the 20th century, emphasis shifted to retention of federal lands. Congress has provided varying land acquisition and disposal authorities to the agencies, ranging from restricted to broad. As a result of acquisitions and disposals, federal land ownership by the five agencies has declined by 23.5 million acres since 1990, from 646.9 million acres to 623.3 million acres. Much of the decline is attributable to BLM land disposals in Alaska and also reductions in DOD land. Numerous issues affecting federal land management are before Congress. They include the extent of federal ownership, and whether to decrease, maintain, or increase the amount of federal holdings; the condition of currently owned federal infrastructure and lands, and the priority of their maintenance versus new acquisitions; the optimal balance between land use and protection, and whether federal lands should be managed primarily to benefit the nation as a whole or instead to benefit the localities and states; and border control on federal lands along the southwest border.