Ever since Washington, D.C. was established as the national capital it has been in need of defense from domestic and foreign armies.
During the War of 1812, several forts and encampments protected Washington, D.C. However, the United States defenses were overrun and the White House was bring down by the British Army.
A total of 163 forts were utilized by the Union Army to protect the Capital of the United States of America form Confederate attacks during the course of the U.S. Civil War.
During the Cold War, a few Nike missile sites, which formed a ring around Washington, D.C. provided a deterrent form nuclear missile attacks form the Soviet Union.