How was the conflict between the Dinka and Nuer people different from the conflict between the Rebels and the Sudanese government?

The Dinka and Nuer, two rival pastoralist groups, have competed over grazing land and water for their cattle in the past. These clashes have usually taken place in a local context without causing massive amounts of fatalities. However, in 2013, the dismissal of the former vice president Riek Machar, a Nuer, by the South Sudanese president Salva Kiir, a Dinka, functioned as a catalyst for mass violence, claiming more than thousand victims.