Anyone interested in peacemaking and poverty reduction should read the new United Nations Environment Program (UNEP) report Sudan: Post-Conflict Environmental Assessment.

This is not just a technical report on Sudan's environment, but a vivid study of how the natural environment, poverty, and population growth can interact to provoke terrible human-made disasters like the violence in Darfur.

When a war erupts, as in Darfur, policymakers look for political explanations and solutions. This is understandable, but misses a basic point. By understanding the role of geography, climate, and population growth in the conflict, we can find more realistic solutions than if we stick with politics alone.

Extreme poverty is a major cause, and predictor, of violence. This is not only common sense, but has been verified by studies and statistical analyses. UNEP says, "There is a very strong link between land degradation, desertification, and conflict in Darfur."

Extreme poverty has several effects on conflict. First, desperation among parts of the population-competing groups struggle to stay alive in the face of a shortage of food, water, pasture land, and other basic needs. Second, the government loses legitimacy and citizens' support. Third, the government may be captured by one faction or another, and use violent means to suppress rivals.

Darfur, the poorest part of a very poor country, fits that dire pattern. Livelihoods are supported by semi-nomadic livestock-rearing in the north and subsistence farming in the south. It is far from ports and international trade, lacks basic infrastructure such as roads and electricity, and is extremely arid. It has become even drier in recent decades due to a decline in rainfall, probably at least partly the result of manmade climate change, caused mostly by energy use in rich countries.

Declining rainfall contributed directly or indirectly to crop failures, the encroachment of the desert into pasturelands, the decline of water and grassland for livestock, and massive deforestation. Rapid population growth-from around one million in 1920 to around seven million today-made all this far more deadly by slashing living standards.

The result has been increasing conflict between pastoralists and farmers, and the migration of populations from the north to the south. After years of simmering conflicts, clashes broke out in 2003 between rival ethnic and political groups, and between Darfur rebels and the national government, which has supported brutal militias in "scorched earth" policies, leading to massive death and displacement.

While international diplomacy focused on peacekeeping and humanitarian efforts to save displaced, desperate people, peace in Darfur cannot be achieved until the underlying crises of poverty, environmental degradation, declining access to water, and chronic hunger are addressed. Soldiers will not pacify hungry, impoverished people.

Peace here can only be sustained with improved access to food, water, healthcare, schools, economic development, and income-generating livelihoods. People and livestock need assured water supplies. In some areas, this can be through boreholes that tap underground aquifers. In other areas, rivers or seasonal surface runoff can be used for irrigation. Elsewhere, longer-distance water pipelines might be needed. The world community will have to help pay for this, since Sudan is too poor to do so.

With outside help, Darfur could increase the productivity of its livestock through improved breeds, veterinary care, collection of fodder, and other strategies. A meat industry could be developed for Darfur's pastoralists to multiply their incomes by selling whole animals, meat products, processed goods (like leather), dairy products, and more.

Social services-healthcare and disease control, education, and adult literacy programs-must also be promoted. Living standards could improve significantly and rapidly through low-cost targeted investments in malaria control, school feeding programs, rainwater harvesting for drinking water, mobile health clinics, and boreholes for livestock and irrigation in appropriate locations.

The only way to sustainable peace is through sustainable development. To reduce the risk of war, we must help impoverished people everywhere meet their basic needs, protect their natural environments, and get onto the ladder of economic development.

Jeffrey Sachs is professor of economics and director of the Earth Institute at Columbia University.