Lucas v. South Carolina Coastal Council

The United States has long been a jealous guardian of its coastal boundaries. Its inaccessibility to foreign invaders has helped keep it safe from outside military forces since the War of 1812. Long before that war, in 1793, Secretary of State Thomas Jefferson formulated a principle that became a legal convention long before it was ever memorialized by statute: that the American "territorial sea" extended to three nautical miles beyond its shoreline. Thus anyone operating a vessel within three miles of America's shores was subject to U.S. law.

The closest America came to foreign invasion after 1812 was during World War II, when cruising Axis vessels on both coasts posed a threat to the nation. After the war was over, President Harry S. Truman in 1945 declared that the territorial sea extended beyond the three-mile limit, all the way to the edge of the continental shelf from which the sea floor rapidly slopes off into deep ocean. Other countries supported this idea--and several asserted their own territorial sea extensions to the continental shelf. This the United States opposed, and over subsequent decades the United Nations would hold three different Conferences on the Law of the Sea (UNCLOS) to adjudicate international disputes about territorial waters and other aspects of maritime law.