Oil and Water in Sudan 211
livestock raiding - both to recoup herd losses and for predatory accumula-
tion - exemplify this pastoralist opportunism.
Technically, range ecologists define disequilibrium environments in terms of
unpredictable and low rainfall whose annual median is less than 400 millime-
tres. The flood plain and its long and short cycles of flood and drought arguably
constitute, certainly in respect to human settlement, a different but equivalent
example of environmental instability. The region's non-linear climatic patterns,
unpredictable levels of flooding for several months (four to six in most areas)
followed by months of drought, biological vectors supporting a variety of
endemic human and livestock diseases, and opportunistic cultural behaviours
combined to foster a uniquely dynamic but often dangerous environment.
Historically, surplus realised from its extremes of fecundity and crisis
resulting from resource shortfall explain the dynamics of human population
growth and movement. Periods of material bounty followed by contracting
resources generated both conflict and the export of excess population to the
savanna region to the south, where immigrants could find conditions suited
to their mixed subsistence economy.34 At a certain threshold [approximately
500 years ago) this pattern of surplus shortfall triggered the periodic migra-
tions of Dinka-like ago-pastoralists to the south.
The impact of strong Nilotic political institutions across large areas of East
Africa via this diaspora attests to conditions of endemic social conflict in the
cradle land. Even Francis Deng35 concedes that Dinka society (and the Nuer
by extension) tolerates high levels of social violence. Apparently the outside
interlopers visiting the spatially isolated region during the early 19'h century
witnessed sufficient jostling among its communities to reinforce the dar d
hnrb designation.
The counterfactual hypothesis mentioned in the preceding section pro-
posed that centrifugal forces rooted in the southern environment, more than
Sudan's ethnic/racial plurality, constitute a major factor sustaining the long-
running conflict. The notion of dar a1 harb, from this perspective, subse-
quently transformed from folk model into ideological justification as the cen-
tralised polity developing at the junction of the White Nile and Blue Nile
began to systematically exploit southern resources.
The Contemporary Nuer-Dinka conflict
We now assess how the complex of ecological variables and historical trends
manifest within the three cycles of the north-south current conflict. This
takes us back to the five variables highlighted in the study's conceptual
frame: competition for scarce resources, ecological sources of surplus value,
distributive agents, ecological trends, and ecological outcomes. The southern
region's environmental-historical pathway identified here establishes a foun-
dation for evaluating the role of these variables across the traditional-con-
temporary continuum.