Why is Abyei contested by Sudan and South Sudan?

The United Nations says at least 75 people have been killed in Abyei. It's a highly contested region, sandwiched between Sudan and South Sudan. While the borders between the two countries were agreed, Abiye was left unallocated. What's the reason behind the ongoing battle for Abyei? Also Mali's military junta have retaken a town held by Tuareg rebels, with the help of Wagner mercenaries. So where does this leave Mali? And the award winning Mozambican photographer Mario Macilau, tells us what inspires him.