Once ethnic conflict breaks out, it is difficult to stop. Massive human-rights violations and physical attacks on civilians—such as rape, torture, mass killings, ethnic cleansing, and genocide—lead to tremendous human suffering. Systematic discrimination and exclusion from national and local political decision making, the appropriation of ethnic minorities’ traditional homelands, and policies that marginalize ethnic minorities are common practices accompanying ethnic conflict.

Even if fought at a low level of intensity, protracted ethnic conflicts have a great impact on the affected society. The lack of functional or legitimate political institutions, weak economic performance, a nonexistent or polarized structure of civil society, and antagonized elites lead to polarization and separation, leaving societies deeply divided and prone to further ethnic strife. In addition, ethnic conflicts have very direct effects far beyond their epicentres. Those involve refugee flows, internal displacement, regional instability, economic failures, environmental disasters, diffusion and spillover effects, and conditions favourable to organized crime and terrorism.

Ethnic conflicts spread in two ways. Diffusion occurs when an ethnic conflict in one state stimulates conflict in another state with similar conditions. Successful movements provide images and moral incentives that result in the motivation and mobilization of other ethnic movements in similar economic and political conditions. Escalation or contagion effects occur when a conflict in one country spreads across borders into neighbouring countries in which an ethnic minority has its kinfolk. That usually involves the engagement of new foreign fighters who are employed by local elites. Ethnic conflicts may start out as intrastate disputes, but they become regional or international crises when foreign powers get involved.

Neighbouring states, regional powers, and international powers are often overwhelmed and unable to deal with international consequences of ethnic conflicts. However, in many cases, those external actors are not passive victims of ethnic crises but actively pursue their own agendas and interests. Foreign sympathizers and diasporas can contribute substantially to a group’s cohesion and mobilization by providing financial, military, political, and moral support. External actors in some cases play important roles in inflaming conflicts or prolonging violent struggles. Opportunistic interventions to gain military, economic, or political benefits take advantage of conflict-affected states and contribute to the conflict. At the same time, international involvement can be crucial in preventing and settling ethnic conflict. The international community plays a role in negotiating, organizing, and supervising cease-fires and peace agreements; investigating past human rights violations; implementing the provisions of peace settlements; conducting peace operations including humanitarian, military, and economic assistance; imposing arms embargoes and economic sanctions; and providing mechanisms that build confidence and capacity and support peaceful means of solving future disputes. Neighbouring states and the international community can thus be victims of the troubles in the region or active contributors—sometimes deliberately, in other cases unintentionally—by providing military, economic, or political support to ethnic groups or by engaging in negotiation and peace implementation. Regional instability is as much a source of ethnic conflict as it is a consequence.