Salva Kiir and Riek Machar loom large over South Sudan's recent history. And they will keep holding the future of the young nation in their hands to a large extent.
So who are they? And what are the roots of their rivalry?
Kiir is the 70-year-old president of South Sudan, a nation of 11 million. Machar, a year younger, is his on-and-off vice-president. The two men have been pivotal figures in negotiating and agreeing, disagreeing and breaking peace agreements over most of South Sudan's first decade as an independent nation.
Their attitudes, behaviour and actions have shaped the country's unwieldy road towards and away from democracy, peace and development, and national unity. To understand South Sudan's contemporary and future political development, security and national unity, it's important to take a closer look at these two towering political leaders.
From rebel fighters to political kingpins
Both Kiir and and Machar spent their formative years in the first and second South Sudanese civil war between South Sudanese rebel movements and the Sudanese armed forces and pro-government militias. These wars were fought between 1955 and 1972, and 1983 and 2005.
Kiir belongs to the Dinka, the largest ethnic group in South Sudan. He was an officer and second in charge in the Sudan People's Liberation Movement/Army (SPLM/A), the main rebel movement and army in South Sudan. He led several successful military offensives against the Sudanese government, for instance capturing large parts of Western Equatoria from Sudanese control.
His military leadership made him popular within the military wings of the movement and he held a strong vision of an independent South Sudan. His vision, however, was in stark contrast to the late John Garang de Mabior, the charismatic SPLM leader who envisioned a united Sudan where South Sudanese had equal political and economic rights along North Sudanese.
A peace agreement between the government of Sudan and the SPLM was eventually signed in 2005, paving the way to South Sudan's independence. Garang became Vice-President of Sudan and president of the transitional government of South Sudan.
Tragically, Garang died in a helicopter crash due to a pilot error in 2005. Kiir took over the SPLM leadership as well as Garang's position as Vice-President of Sudan, and became the president of South Sudan. After a landslide referendum in 2011, South Sudanese were granted independence.
Kiir is generally known for his calm, mild tempered, and rather emotionless public appearances. But even during his years as subordinate to Garang he had a thirst for formal authority and power which he has expanded with stamina within the SPLM and South Sudanese state institutions over the past decades.
Machar belongs to the second-largest ethnic group in South Sudan, the Nuer. He was a regional commander under Garang's leadership in the SPLM during the 1980s. Like Kiir, he disagreed with Garang's objectives, preferring an independent South Sudan. He also complained about Garang's authoritarian leadership. After the 2005 peace agreement and Garang's death, Machar became the Vice-President of South Sudan.
The genesis of violent rivalry
Frustrated with and opposed to Garang's leadership of the South Sudanese resistance, Machar and members of other tribes formed an opposition rebel movement to the main rebel group SPLM in 1991. This they called the SPLM-Nasir faction.
Machar and his Nasir faction fought for South Sudanese independence. But at the same time they received financial and military support from the military government in Khartoum, the main opposition of the SPLM. Relying on a divide-and-conquer strategy, Khartoum used Machar and his troops to turn against the SPLM rebels including Garang and Kiir.
During one known massacre in the town of Bor, Nasir troops killed thousands of civilians belonging to the ethnic Dinka, Kiir's tribe. The result were reprisal attacks. Divisions within South Sudan became not only increasingly violent but were also increasingly ethnic in character.
The legacy of this ethnic violence remains largely unresolved and unaddressed. It continues to be a source of latent distrust and suspicion that's exploited by political rhetoric and manipulation.
Since 2013 South Sudan has been embroiled in a civil war that is essentially a conflict between Kiir's Dinka-dominated troops and Machar's Nuer-dominated troops. Both Kiir and Machar are concerned about their own political future, their own security and that of their families and allies and ethnic kin.
The United Nations Mission in South Sudan (UNMISS) has the mandate to support the implementation of several peace agreements as well as to protect civilians. It has a large presence: more than 14,000 military personnel, 1,500 police and at least 2,000 civilian staff. Nevertheless, it has often been perceived as doing too little too late to protect civilians.
The Dinka and the Nuer
Ideologically, Kiir and Machar do not seem to be that far apart. They have both always seen South Sudan's future as that of an independent nation. The difficulty lies in agreeing on how to organise, distribute and cooperate within a nation that consists of dozens of ethnic groups and sub-tribes, different livelihoods, and cultural links across neighbouring countries.
It is clear, although they would never admit it, that the two men see themselves and their ethnic communities as the main heirs of the nation, and that they each hold a legitimate claim to leadership. These claims are nurtured through the relative population share of both groups and their role in the war with Sudan, largely due to their settlement areas along the South Sudan-Sudan border.
The Dinka are the largest ethnic group in South Sudan, representing around 35% of the population. The Nuer are the second largest with around 16%. Other groups represent much smaller shares.
In recent years, foreign aid has been cut back to humanitarian assistance, foreign investment has stalled due to insecurity, prices for everyday goods have skyrocketed due to reduced agricultural activities and increased import reliance.
These are just some of the things that make life for ordinary citizens in South Sudan harder than it already has been for most of their lives. At the end of the day, the question for Kiir and Machar is what legacy both want to be remembered for.
Author: Carlo Koos - Associate Professor of Political Science, University of Bergen