The big triangular portion of Mali that makes up the northeast two-thirds-ish of the country has been the subject of rebellions and independence movements for as long as Mali has been independent in its post-colonial period. That area is the really hot and dry part of an already hot country, and is generally home to Tuareg and Songhai people.
The government of Mali since the 2021 coup has been working with Wagner, and at some point last year the ceasefire broke. The Malian government says that the rebels weren't complying with the 2015 Algiers accords, the rebels say that government and Wagner forces massacred hundreds of civilians. The war starts up again, and so now there is the above incident in which the rebels gave Wagner a kicking