Mauritania–Western Sahara border

[3][2] The entire French West Africa-Saguia el Hamara/Rio de Oro boundary was confirmed by treaty on 19 December 1956, with France and Spain then demarcating it on the ground in 1957 with several pillars.

[2] A railway was built in 1960-63 which paralleled the southern half of the boundary, including an expensive tunnel through an escapement north-west of Choum constructed so as to order to avoid the right-angle of the south-eastern Spanish Sahara.

An International Court of Justice ruling on the matter in October 1975 stated that neither the Moroccan nor Mauritanian claims to Western Sahara were strong enough to justify annexation, and that the Saharawi people should be allowed to determine their own future.

[7][2] Morocco thereafter sought to settle the matter militarily, and in November 1975 conducted the 'Green March', in which thousands of soldiers and Moroccan nationalists forcibly crossed the Morocco-Spanish Sahara border.

Polisario forces declared a Sahrawi Arab Democratic Republic based on the boundaries of Spanish Sahara, thus starting a long war against Morocco and Mauritania.

[8] In the south the wall parallels the southern straight line section of the border out to the sea, effectively abandoning the Western Saharan half of the Ras Nouadhibou peninsula; at present Mauritania retains a military presence in the area.