Britain and France drew nearly 40% of the world's international borders
By one estimate, Britain and France traced close to 40% of the total length of the world's international boundaries. That colonial legacy explains why so many borders in Africa, North America and the Middle East run ruler-straight, ignoring rivers, mountains and the peoples living on either side.
A border is a geographic boundary, set either by nature, such as oceans and mountains, or by governments at every level from nations to provinces. Political lines arise through war, colonisation or agreement. Some are wide open, like most internal boundaries or those inside Europe's Schengen Area, while most national frontiers can be crossed legally only at checkpoints, with airports and seaports counted as borders too. International law generally lets each country set its own conditions for entry. Strictly, the border is the line itself, and the surrounding area is the frontier.
Borders used to be fuzzy. Pre-modern usage could mean either side of a boundary, hence words like borderline and borderland, and because royal power faded with distance from the capital, rugged border country sheltered outlaws. Contested strips known as marchlands lay between rivals; modern holdovers included neutral zones shared by Saudi Arabia with Iraq from 1922 to 1991 and with Kuwait from 1922 to 1970.
Natural borders follow obstacles to travel. Oceans are so costly to govern across that few countries span continents; river boundaries are often drawn precisely along the thalweg, the deepest channel, and mountain borders tend to follow drainage divides. As transport improved, such barriers mattered less, so newer borders in Africa and the Americas track nature less than old ones in Europe and Asia. Geometric boundaries instead follow straight lines or arcs; the Canada–United States border runs along the 49th parallel for about 3,500 km from Lake of the Woods to the Pacific. In the 11th century China's Song dynasty even engineered a defensive forest as a landscape border.
Old lines can outlive their legal life. The former boundary between East and West Germany still shows in the landscape and economy, as do the defunct dividing lines of Vietnam, gone since 1975, and Yemen, gone since 1990. Borders also extend beyond land: maritime zones recognised under the UN Convention on the Law of the Sea govern ocean resources, and national airspace reaches 12 nautical miles from the coast, with the vertical limit commonly placed at the Kármán line, 100 km up, where outer space begins.
Source: Border
