Machar is the General making war in South Sudan against the government.
Museveni the president of Uganda, South Sudan’s southern neighbour had warned Machar that East African countries would unite to defeat him militarily if he does not agree to attend peace talks.
Some analysts say Museveni distrusts Machar and that stems, in part, from the latter’s alleged links to the Ugandan warlord Joseph Kony, who once operated in jungles that now fall in South Sudan’s territory and with the alleged support of Sudan’s government.
In 2005, as South Sudan moved closer to autonomy, Kony agreed to negotiate with Uganda’s government under the mediation of Machar. Those talks failed and, in late 2008, Kony and his top commanders fled their base in the forests of east Congo only hours before Uganda’s military moved in to launch an aerial assault. Some in Uganda’s military believe Machar warned Kony of the impending attack.
http://www.theguardian.com/world/2014/jan/08/south-sudan-peace-talks-falter