What does the U.S. border?

The contiguous United States borders Canada to the north, Mexico to the south, the Atlantic Ocean to the east, and the Pacific Ocean to the west, with additional borders for non-contiguous states (Alaska borders Canada and the Arctic Ocean and Pacific Ocean; Hawaii is surrounded by the Pacific Ocean). The total perimeter of the contiguous United States is about 12,034 miles, including 5,525 miles of border with Canada, 1,954 miles of border with Mexico, about 2,069 miles of Atlantic coastline (including the Gulf of Mexico), and about 1,293 miles of Pacific coastline. Adding Alaska brings about 6,640 miles of Alaska Pacific and Arctic coastline plus a 1,538 mile border with Canada. Hawaii adds about 750 miles of coastline.

The U.S.-Canada border is the longest international land border in the world, established by a series of treaties. The eastern portion follows the St. Lawrence River, the Great Lakes, and various rivers and treaty lines from Maine to Lake of the Woods, Minnesota. The western portion follows the 49th parallel of north latitude from Lake of the Woods to the Strait of Georgia, then dips south to surround Vancouver Island, established by the Convention of 1818 (for the eastern part) and the Oregon Treaty of June 15, 1846 (for the Pacific Northwest). The Alaska-Canada border was established by the Alaska Treaty of 1867 and refined by various surveys and the Hay-Herbert Treaty of 1903.

The U.S.-Mexico border runs along the Rio Grande from the Gulf of Mexico to El Paso, then west along surveyed lines through New Mexico, Arizona, and California to the Pacific just south of San Diego. The Gadsden Purchase of December 30, 1853 set the southern boundary of New Mexico and Arizona. The Atlantic coastline runs from the Canadian border at Maine south to the Florida Keys, including the Atlantic coast proper plus the Gulf of Mexico coastline of Florida, Alabama, Mississippi, Louisiana, and Texas. The Pacific coastline runs from the Canadian border at Washington south to the Mexican border at California. The contiguous 48 states span about 2,800 miles east to west and about 1,650 miles north to south.

The borders shape American politics, economy, and security. Major issues include trade (the United States-Mexico-Canada Agreement effective July 1, 2020); immigration (especially across the southern border); drug trafficking; environmental cooperation (Great Lakes water quality, Pacific fisheries); and security (NORAD, Customs and Border Protection). The two ocean coasts also frame American economic and cultural orientation. The Atlantic coast historically faces Europe and Africa; the Pacific coast faces Asia and the Pacific Islands.