The member states of the African Union are the 54 sovereign states that have ratified or acceded to the Constitutive Act of the African Union to become member states to the African Union (AU). The AU replaced the Organisation of African Unity (OAU), and AU membership was open to all OAU member states. From an original membership of 36 states when the OAU was established on 25 May 1963, there have been eighteen successive enlargements – the largest occurring on 18 July 1975 when four states joined. South Sudan is the newest member state, having joined on 27 July 2011. Currently, one member state, Central African Republic, is suspended due to a coup d'état and political struggles. The only African United Nations member state which could join, or more precisely re-activate its membership, is Morocco, which withdrew following the organizations acceptance of the Sahrawi Arab Democratic Republic, whose status is disputed, as a member state. Spain, primarily a European country, maintains sovereignty over Spanish North Africa and the Canary Islands off the coast, but is only accredited to the African Union.