With this last piece of the jigsaw now in place, does it mean that African unity has finally been achieved? Or is the current picture of the AU likely to be ephemeral?
The criteria to become a member of the African Union are simple. The organisation is open to all African states and accession requires approval by a simple majority of the existing members. Though being an African state seems a straightforward requisite, there is ample room for interpretation.
Take for example efforts by Haiti, a Caribbean state, to accede to the union. This would require the AU review its reading of pan-Africanism. Other possible new members are states that could be formed as result of secession as well as European overseas territories that are part of Africa but represent the last vestiges of imperialism.
The dominant view of the AU reduces Africa to its continental definition. Accordingly, the objective is the political union of the African landmass and the adjacent islands.
This view has been used in relation to Haiti. The country has sought membership since 2012 on the grounds that it was the first black republic in history. Though perceived by many as belonging to Africa culturally, the AU rejected the island's application in 2016 on the grounds that it was not an African country.
But there are other interpretations of pan-Africanism. One view, for example, is that the African diaspora is an integral part of the continent, another is that racial identity - in the sense of négritude - or cultural identity makes people eligible for African citizenship.
Even within the narrow continental vision of pan-Africanism, there is still room for new members. Somaliland is one potential future candidate. It broke away from Somalia in 1991 and has acquired state-like functions, such as the autonomous provision of public goods, and is a potential candidate for membership. But, for the time being all AU member states view it as a part of Somalia. None recognises it as a state.
Other secessionist movements, such as the Barotseland kingdom that transcends Zambia, could also gain independence from current nation states. New states based on the geographic imagination of pre-colonial borders could form and eventually request accession to the AU.
Africa's "last colonies"
The AU understands Africa as a sealed off geographic entity. Yet it remains remarkably quiet about the many bits that are geographically part of the continent but do not consider the AU their home. Take the European overseas territories which include:
Portugal's Madeira, and
The "last colonies" could in principle exercise self determination and join the AU after successful independence. Yet, that seems highly unlikely in the near future given the overwhelming sense of belonging to a European country.
Inclusion is not the only issue facing the African Union. Some existing members could also withdraw. The union's Constitutive Act makes provision for cessation of membership - a procedure that only requires a written request and a one year waiting period.
Countries seeking a binding federalist union, such as Libya under Gaddafi, unsuccessfully opposed this exit option, though in practice only Morocco ever left the organisation.
But others could consider doing so.
Take Cape Verde. In 2007 the European Union and the island nation off the coast of Senegal established a special partnership that prepares it to qualify for future accession talks with the EU. This would entail it exiting from the AU.
In the Comoros there have been movements to replicate the experience of Mayotte to join France. Though these have been met with resistance by both the Comoros government - who fears secession - and France - who fears costs - an exit remains conceivable.
More perils for AU membership lurk where countries are part of competing regional organisations, such as the Arab League or the Community of Portuguese Speaking Countries. These offer identities transcending the continent and should they become more binding members will have to choose between them and the AU. In particular the European Neighbourhood Policy is designed to increase the magnetic pull of the EU for North Africa.
The AU Constitutive Act makes no provision for expelling members. Only suspension is foreseen in cases when a government has come to power trough unconstitutional means. However, with a two-thirds majority, AU members could vote to introduce a provision for expelling.
Should that happen, the Sahrawi Arab Democratic Republic (SADR) would be first on the list. In the past, most African states considered Moroccan occupation of the Western Sahara a form of colonisation. They legitimised the claim of the SADR to govern the Western Sahara, which triggered Morocco's exit in 1984.
But the tide is turning.
The growing support within the AU for Morocco despite its occupation of the Western Sahara makes a dismissal of the SADR more likely. It also indicates that anti-colonialism has lost vigour, which reduces the likelihood of an assertive claim by the AU to the "last colonies".
The AU's narrow geographic interpretation of Africa seems to have reached its zenith with the accession of Morocco. But important inconsistencies remain. The AU is likely to come under pressure in the future to review its reading of pan-Africanism, both from inside and outside the continent.
It took Morocco 33 years to rejoin. Over the coming 33 years, the AU's shape is likely to continue changing. We have not seen the end.
Frank Mattheis does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.