The war in Darfur, Sudan (2003-present) has received considerable media attention as a primary example of mass violence in conjunction with adverse climate change (Ban Ki Moon, 2007). It can roughly be broken down into three conflict dimensions: the first opposing the Government of Sudan to various rebel groups fighting for the regional autonomy of Darfur, the second opposing different local groups, which compete over land use and are often divided along an Arab-African and/or farmer-herder dichotomy and the third defined by factional disputes within the rebel groups (see Communal conflicts in Darfur). Fighting between these groups and the government as well as mass violence against the civilian population has led to several hundred thousand direct and indirect fatalities and more than 2.5 million displaced people (UCDP, 2014; Auswärtiges Amt, 2012). Two multilateral military interventions have been conducted in Darfur without succeeding in ending the violence. The humanitarian situation on the ground remains difficult.

A climate culprit in Darfur?
Originally, the war in Darfur evolved out of rebel groups’ struggle against the economic and political marginalization of Darfur by the central government in Khartoum. Yet, it became rapidly intermingled with local conflicts over resources, whose origins can partly be traced back to the Sahelian droughts of the 1970s and 1980s. Whether these droughts were caused by anthropogenic climate change or instead resulted from natural climate variability is still a matter of scientific debate (see for instance Niang, Ruppel, Abdabro et al., 2014). Claims about a direct link should therefore be considered with caution, even if they come from very respectable sources such as the current Secretary-General of the United Nations, Ban Ki-Moon (2007). Yet irrespective of this scientific debate about climate change versus climate variability, the Darfur case is illustrative of how conflicts may develop when societies are unable to adapt to the consequences of climatic changes with peaceful means. And these lessons matter because there is strong evidence and scientific agreement that climate change will generally bring about intensifying and more frequent droughts, despite the uncertainty about the causes of any single event such as the 1980s drought in the Sahel.

Drought, migration and resource competition
Prior to 2003, Darfur had already witnessed several armed clashes between different local groups, most often divided along an Arab-African and/or farmer-herder dichotomy and mostly revolving around issues of competing land use. These conflicts were driven to an important part by deteriorating environmental conditions in the Sahel and the need for northern pastoralists to relocate further south, into areas mainly inhabited by settled farmer communities (De Waal, 2007a). Rainfall in Darfur had constantly been declining in the 1960s, 1970s and the first half of the 1980s, culminating with the drought and famine of 1984/85. Nomadic pastoralists living in the northern part of the region were hit particularly hard, whereas populations in the southern part of Darfur were somewhat less severely affected. During the 1980s and the 1990s, a high number of northern pastoralists thus relocated further south, into areas mainly inhabited by settled farmer communities (De Juan, 2015). At that time, the southern part of Darfur was already experiencing mounting pressures on local resources, due to natural population growth and an influx of migrants from neighboring Chad. In combination with increased migration from northern Darfur and the gradual abandonment of traditional fallow systems, these factors led to a vicious cycle of overexploited soils, deforestation and further depleted resources (De Waal, 2007a; Leroy, 2009).
 
Weakened institutions and 'divide and rule' politics
This adverse development was accompanied by the progressive weakening of customary land management institutions. The Hakura system, traditionally responsible for allocating land and coping with drought, came under stress, both by the reduced availability of land, and by efforts of the central government in Khartoum to nationalize unregistered land in Darfur. The following nationalization process created opportunities for northern pastoralists to circumvent customary law and extend their claims on the land of southern farmers, encouraging farmer-herder violence (Unruh & Abdul-Jalil, 2012).
The situation was such that an increasing number of Darfurians grew discontent with the central government in Khartoum, which did little to avert famine and quell disputes between migrants and residents. To the contrary, its ham-fisted counter-insurgency tactics often revolved around what Sudan expert Alex de Waal (2007b:1039) has described as ‘Khartoum’s penchant for addressing local conflicts by distributing arms to one side to suppress the other’. 

'Arab' - 'African' divide
Matters were further compounded by a racist discourse affirming the superiority of ‘Arab’ groups over ‘African’ groups, which was both encouraged by elites in Khartoum, and a pan-arabic nationalism propagated by Libya’s Muammar al-Qaddhafi. Grievances over structural inequalities between Darfur and the central regions of Sudan had collectively been shared by different Darfurian groups and are a major reason for the formation of the ‘Sudan Liberation Movement/Army’ (SLM/A) and ‘Justice and Equality Movement’ (JEM) and their struggle for regional autonomy. Increasing ethnic polarization created however new divisions within Darfur, which could be exploited by the government in order to weaken the Darfurian rebels (see Conflict between Masalit and Reizegat Abbala). This explains the dual nature of the war in Darfur, as both a war about autonomy and an inter-ethnic conflict.