What are the origins of global conflict, whether historical or contemporary, among nation-states or other actors? How have peace and justice movements evolved in response?
The Greenwood Encyclopedia of International Relations by 
Historical Dictionary of U. S. Diplomacy from the Civil War to World War I by 
U. S. Diplomacy from World War I Through World War II by 
Historical Dictionary of U. S. Diplomacy since the Cold War by 
Sipri Yearbook: Armaments, Disarmament, and International SecurityThere are specialized encyclopedias in the reference section covering major world conflicts, including World War I and World War II as well as the Civil War, the Vietnam War, and the Korean War. These tend to emphasize military history but include some social history as well.
Encyclopedia of Modern Ethnic Conflicts by 
The Encyclopedia of War by You will find encyclopedias covering countries and regions of the world including Africa, the Middle East, and East Asia as well as this work covering issues and countries.
Encyclopedia of the Developing World by 
Violence in America
Encyclopedia of American Civil Liberties by 
Encyclopedia of the U. S. Government and the Environment by 