The burning of Riek Machar's hometown of Leer marks at least one violation of the 'cessation of hostilities' agreement.
Uganda seeks to be a regional power, is militarist and prone to adventures. It fought the rebels in S. Sudan and its troops could jeopardize a peace deal there.
The Sudan People's Liberation Army was always a multi-ethnic liberation movement against Omar Al Bashir's Sudan, not a coherent party. Now it seems a venue for warlords.
Former allies in its war for independence have turned on each other and the world's youngest nation faces the danger of a prolonged war. What you need to know about the conflict.