What is the Western Sahara?
The disputed Western Sahara region, which has significant phosphate reserves and offshore fishing, is situated in north Africa between Morocco, Mauritania and Algeria.
In 1975, colonial power Spain, that had governed the Western Sahara, left the region. Shortly after Spain left, war broke out.
Morocco believes that the area is part of its sovereign land. The region has also been claimed by the Polisario Front, a guerrilla group fighting for a separate state, since 1975. The Front also claims to be the sole representatives of the Sahrawis; it has received support from neighbouring Algeria.
Why did Morocco quit the African Union?
33 years ago, Morocco quit the AU's predecessor, the Organisation of African Unity because of the Western Sahara. Earlier this year, it rejoined the pan-African body.
The AU had recognised the Western Sahara – or Sahrawi Arab Democratic Republic (SADR) as an independent nation back in 1982 – and Morocco wasn't happy about it.
"Africa is my home and I am coming back home," King Mohammed said in January's AU summit. "I have missed you all. Africa is indispensable to Morocco and Morocco is indispensable to Africa."
What made Morocco come in from the cold?
Support for Western Sahara as a nation has ebbed over the past few years because of the growing importance of Morocco's $110 billion economy – the fifth largest in Africa.
Since 1991, Rabat has held onto its own plan for the area's autonomy.
How did Sahrawis respond to Morocco's readmission?
Sahrawi Foreign Minister Salem Ould Salek described the AU's admission of Morocco as a "major step" towards full international recognition since it would now be in the same room, on equal terms, with its rival.
"From the moment Morocco did not set conditions on its return, we take their word and we accept that Morocco is admitted to the African Union," Salek said.
"It's a positive step for the people of Western Sahara," he added. "After 33 years, Morocco has realised that it has to sit with the Sahrawi Republic. We hope that Morocco will have the goodwill to resolve this conflict and withdraw its troops."