What is the longest border between two countries?

What is the longest border between two countries? The answer is the Canada–United States border.

The boundary measures about 8,891 kilometres in total, making it the world’s longest international border. It includes Canada’s border with the contiguous United States and its separate border with Alaska, which lies northwest of Canada.

The border was shaped by several agreements, including the Treaty of Paris in 1783, the Treaty of 1818, the Webster–Ashburton Treaty of 1842, and the Oregon Treaty of 1846. It crosses forests, prairies, mountains, lakes, rivers, and the Great Lakes.

The familiar phrase “the 49th parallel” is only partly accurate: sections follow that latitude, but the boundary also bends around waterways and uses other surveyed lines. Another common confusion is Russia–Kazakhstan; that border is very long, but the Canada–United States boundary is longer when its Alaska section is included.