As I have already discussed Algeria’s reasoning on the Mauritania coup, it is appropriate to discuss Morocco’s. From what I can tell, Morocco has three main priorities in Mauritania: (1) Avoiding the possibility of “chaos” on its southernmost borders, (2) avoiding the return of Sidi, and (3) asserting itself as a regional problem solver and power broker. Their primary assumption seems to be that despite their overwhelming displeasure with the coup, no world power is so strongly interested in the country as to forcibly restore the previous government. Eventually, the world will accept the coup as a fact of life and they will normalize their policy towards the junta. Thus, it is best to cultivate a favorable disposition in the regime presently in place so that when the rest of the world does reconcile with the junta, which would ideally take place by way of Morocco, the Mauritanians will have to pay the Kingdom back in some manner or the other.
Thus, their offer yesterday to assist the Mauritanians in easing up the Western position on the coup. If their strategy works, Sidi, whom the Moroccans saw as hostile to their position in the Sahara, will not come back, regardless of the efforts of his PM or of other domestic and international actors. The junta (or whomever takes its place, assuming the said transition flow from it, and not against it) will therefore be inclined to take a less hostile stance toward Morocco in on the Sahara.
The prospect of the total break down of order in Mauritania, either by way of civil war, warfare with al-Qaeda or the like, is not especially likely, but always a possibility. Moroccan fear is twofold: The break down of order in northern Mauritania would mean the expansion of areas from which the Polisario could operate, as there are tribal and political sympathies for the organization there, and the region could also become an area from which al-Qaeda or other international criminal networks could operate. The Moroccans evidently believe that Abdel Aziz is the best candidate to ward of such misfortune. By supporting him they gain a potential ally, a couple of prestige points, and move the balance of power in the region away from Algeria. (It should also be noted that Senegal, a Moroccan ally, also has yet to condemn the coup.)
If this works, the Moroccans will have cause for celebration. If it fails they will find themselves ever more isolated from Africa, once again positioning themselves on the other side of the law and order discussion. And they will have tossed the Mauritanians back to the Algerian side of the Sahara debate.