As noted earlier, the Darfur crisis represents a complementarity of four conflict types-a communal conflict (Chapter 3), a conflict of local elites (Chapter 4), a center-periphery conflict (Chapter 5), and a cross-border conflict. This chapter addresses the fourth conflict type-cross-border conflicts in which neighboring countries intervene in the Darfur crisis. For many protracted violent conflicts, the scope of hostilities expands beyond the bounds of the original fighting, spreading to neighboring regions or countries, intensifying the scale of the violence, and consuming large segments of the civilian population in its wake. This cross-border conflict is particularly prominent in Africa, in part because of the artificial nature of the national borders. Consider the Great Lakes region of Africa, where clashes in one country are often followed by periods of intense violence in neighboring countries. For example, warring factions in the Rwandan genocide in 1994 continued their struggles in the Democratic Republic of Congo for many years. The cross-border dimension of conflicts usually takes one of two forms-first, when troops from neighboring countries are directly engaged in conflict with its own forces, and second, when one party acts via a proxy, not engaged directly in the fighting but instead fighting via another actor. Chad and Sudan have been engaged in a proxy war in which each government has exploited other military forces for its own partisan goals, each casting these forces as substitutes for its campaign against the other government. Such a war has a direct impact on Darfur.