Canada–United States border 3.99

The Canada–United States border, officially known as the International Boundary, is the longest international border in the world between two countries. It is shared between Canada and the United States, the second- and fourth-largest countries by area, respectively. The terrestrial boundary is 8,891km long, of which 2,475km is Canada's border with Alaska. Eight Canadian provinces and territories, and thirteen U.S. states are located along the border.