Oil and Water in Sudan 207The expansion led to a fourfold increase in Nuer territory between 1818 and
1890, to a total area of 35 000 square miles - prompting Kelly to term it as "one
of the most prominent cases of 'evolutionary success' contained in the ethno-
graphic record':I6 According to him the inflation of the traditional bride price
paid in cattle fuelled this phenomenal expansion. Kelly's and other structural
hypotheses, however, become sui generii secondary explanations after factoring
for how ecological conditions within the flood plain favoured the Nuer livestock-
based economy.
This statement provides a theoretical template for focusing on the demo-
ecological causes of social behaviour and change. Demographic processe$
and ecological trends provide basic criteria for analysing Dinka and Nuer
conflict over time. Insofar as their resistance is a central factor in the civil
war, these processes, trends, and evolving differences among groups help us
assess the political ecology of the current conflict.17
Several historical caveats are in order before we examine the ecological
dynamic underpinning the flood plain conflict system.
The greater flood plain region as the Nilotic cradle land is the source of
periodic out-migrations over the past two thousand years. Ancestors of the
present-day highland Nilotes are believed to have left during the first millen-
nium AD; the plain's Nilotes began trickling out over 1 000 yean ago. Major
movements of the river-lake Nilotes, Lwo-speaking peoples who share the
most direct linguistic links to the Dinka-Nuer-Shilluk complex, occurred over
a period of some 500 years prior to 1840.
These 'migrations' likely involved small groups, clans, and even clusters of
households who probably moved only small distances at a time; in all
instances they trekked to the south, settling a large swath of present-day
Uganda and Kenya. Archaeological evidence indicates the earliest peoples to
depart relied upon foraging and fishing; later emigrants were agro-pastoral-
ists. The pattern of migrations generally follows the onset of drier altema-
tions in the long climatic cycles.
Herring obsewes that "the position of the early Luo homeland[s) cannot
be determined with any precision, but it seems likely that it was on the flat
swampy clay plains in the south-cenual Sudan, and/or on some of the larg-
er ridges within this region, and/or on the more elevated periphery of the
Ironstone Plateau':I8
This prompts us to infer that the flood plain and its environs are, despite
the difficulties associated with its alternating extremes of flooding and dry-
ness, a fecund and resource-rich area supporting higher population growth
than other areas over the long term. The robust population growth during
wetter times would have naturally led to conflict during drier cycles when
biotic resources decline. For a long time out-migration provided an outlet for
when population exceeded the environmental carrying capacity, but during
the 1700s most areas to the south were effectively filling up.19