Generally, and on principle, international peacekeeping efforts fall under two main theories: liberalism and constructivism.  Under the United Nations, peacekeeping efforts are used as an attempt to create a stable environment where warring factions are able to negotiate.  In order to achieve this however, it is imperative and essential that both parties are willing to negotiate with one another. 

These efforts follow the ideology of liberalism that while the world is in a state of anarchy, international organizations and the interdependence of states can create a peaceful environment.  On an individual level, while both external and civil war may bring out the baser tendencies of people, the peacekeeping efforts work to bring out the positive attributes in warring people, therefore allowing them to establish a solution that satisfies both parties. 

From a constructivist’s view, peacekeeping efforts are a way to reach a middle ground between warring factions whose cultures or identities are in conflict with one another.  By relating the importance of cooperation and peace to people of different backgrounds and cultures, the United Nations seeks to create an environment where different people can work together despite their differences or antagonistic histories towards each other.           

However, in the context of a realist’s “self help” world, countries at war will often manipulate the United Nations peacekeeping efforts by stealing supplies and aid sent to refugees and exploiting structures, such as roads, built by peacekeeping forces.

Source: http://www.cato.org/pubs/fpbriefs/fpb-034.html