Shatt al-Arab
The Shatt al-Arab (also called the Arvand Rud in Persian) is a river in Southwest Asia of some 200 km in length, formed by the confluence of the Euphrates and the Tigris in southern Iraq. At the southern end of the river it constitutes the border between Iraq and Iran down to the mouth of the river as it discharges into the Persian Gulf. Conflicting territorial claims and disputes over navigation rights between these two countries were among the main factors for the Iran-Iraq War that lasted from 1980 to 1988, when the pre-1980 status quo was restored. The city of Basra along this river is Iraq's major port.
Control of the waterway and its use as a border have been a source of contention between the predecessors of Iran and Iraq states since a peace treaty signed in 1639 between the Persian and the Ottoman Empires, which divided the territory according to tribal customs and loyalties, without attempting a rigorous land survey. The tribes on both sides of the lower waterway, however, are Marsh Arabs, and the Ottoman Empire claimed to represent them. Tensions between the opposing empires that extended across a wide range of religious, cultural and political conflicts, led to the outbreak of hostilities in the 19th century and eventually yielded the Second Treaty of Erzerum between the two parties, in 1847, after protracted negotiations, which included British and Russian delagates. Even afterwards, backtracking and disagreements continued, until British Foreign Secretary, Lord Palmerston, was moved to comment in 1851 that "the boundary line between Turkey and Persia can never be finally settled except by an arbitrary decision on the part of Great Britain and Russia". A protocol between the Young Turks and the Persians was signed in Constantinople in 1913, but World War I cancelled all plans.
The British advisors in Iraq were able to keep the waterway bi-national under the thalweg principle, that has worked in Europe (see Danube River): the dividing line was the middle of the waterway. All United Nations attempts to intervene as mediators have been rebuffed.