People get worked up over this topic. I hope I have been impartial.
Many current atlases and maps, not least Google Maps (left), identify a territory called ‘Western Sahara’. The dashed border along its northern edge gives a hint that there is no actual country called ‘Western Sahara‘. The 2014 map by the British FCO (above right) gives a slightly more accurate representation of how this this area breaks up, though their red zone unhelpfully covers the regular and open border crossing from Morocco into Mauritania on the Atlantic Route.
The former Spanish colony of Spanish Sahara, (left) was relinquished by Spain in favour of Morocco and Mauritania in 1975, ignoring the wishes of the indigenous and largely Arabic Saharawi (‘Saharans’) inhabitants and the Polisario organisation which had been agitating for independence since the 1960s. In 1976 the Saharawi Arab Democratic Republic (SADR) was declared by the Polisario soon after Spain moved out.
By 1979 Morocco had annexed the resource-rich west of the territory to which it had long made claims. As a result of that, a war broke out with Algeria (allied with Mauritania for a while) who claimed to support the Saharawi and SADR.
In 1991 the UN brokered a ceasefire and a referendum to decide the future of the Saharawi. MINURSO bases are still dotted around the territory – (a 2014 MINURSO map is here. But by that time Morocco had populated its part of the territory with Moroccans to win any referendum which has been repeatedly postponed since then. Layounne today has a population of some 200,000.
In the meantime Morocco built a huge 2000-km long militarised wall or Berm dividing the territory longitudinally (above left and right), like a modern Great Wall of China, The Atlantic side is Moroccan controlled. East of the Berm as far as the Mauritanian border is the Polisario Free Zone (PFZ), supported by Algeria which also hosts many Saharawi refugee camps over the border in nearby Tindouf, Algeria.
From Google maps you can see the Berm cut a corner off northwest Mauritania for about 50km (left), so dividing the PFZ into two regions. Not all maps on this page accurately show this delineation and who knows if this is a former ‘forward line’ of the Berm which is not currently manned. It is almost certainly mined. Whatever, it forces the Saharawi of the PFZ to cross into Mauritania in the vicinity of Bir Mogrein when they want to get from one region to the other. One can speculate that the Mauritanians tolerate these transits as long as the non-Mauritanian Saharawi (ethnically Moors, anyway) stay north of a certain area, well north of Zouerate. Further south one hears the border between the PFZ and Mauritania is respected by the army and police of both sides, although it’s said Saharawi/Moorish nomads seasonally pass over the border and back.
What does this all mean to the desert traveller?
You can pass down the all-sealed Atlantic Route in Moroccan-controlled Western Sahara to Mauritania (left) with no problems bar a few checkpoints. Fuel is discounted south of Tan Tan and larger towns include Layounne and Dakhla.
Inland, pistes lead to mines, small Saharawi settlements as well as Moroccan installations embedded along the landmined and patrolled Berm. Zoom in with Google sat and you can see these installations clearly. Off roaders do travel in this area (well away from the Berm) and there’s even a French guidebook listing routes (right). But the rather dull landscape and slight risk of landmines when away from well-used pistes puts people off.
The Dakar Rally used to cross from Smara or Guelta Zemmour in Morocco, briefly across the PFZ and into northern Mauritania, but since at least 2002 tourists cannot cross the Berm – formerly with least difficulty along the main piste linking Guelta Zemmour and Bir Mogrein.
A couple of travellers have traversed the PFZ’s southeast corner which is used by locals as a shortcut between Nouadhibou and Zouerat to avoid the Azzefal dunes (left). But as a foreigner, once noticed or arriving at Zug you may be escorted via a couple of UN-bases northeast to Arounit close to the Mauritanian border and just south of Zouerat.
In the PFZ you’ll find Spanish more commonly spoken than French and it’s said you can get by with no visa or invitation letter, use Mauritanian ouguiya and buy cheap Algerian fuel.
A 2017 report from the area.