Peace operations cover a wide range of activities that are needed in the sort of low-intensity conflict that may take place after the end of a conventional war between nation-states, a civil war, or a state that has broken up into local militias. Other terms are used in national doctrine, such as stability operations by the United States and low-intensity conflict by the United Kingdom.
The terminology is sufficiently vague that termss are not consistently written: "peacekeeping vs. peace keeping", "peacemaking vs. peace making", etc. Only "peace enforcement" seems always to be written as one word.
While every situation is unique, several types of activity are known:
- Peace keeping: this involves having neutral observers separate the parties in dispute. The observers may or may not be armed. If armed, they are unlikely to be authorized to use weapons other than in self defense. This is a traditional United Nations role under Chapter VI of the United Nations Charter.
- Peace enforcement: From the United Nations standpoint, this is a Chapter VII military operation. In Thomas Barnett's paradigm, if the area in conflict is occupied, or in civil war, a leviathan, or first-world military force that takes down the opposition regular forces. Leviathan is not constituted to fight local insurgencies, but major forces. Leviathan will be replaced by system administrator (see below).
- Peace making: often through third-party mediation but preferably direct negotiations, this is the process of developing the consensus of the shape of peace, to be formalized by diplomats and politicians. The mediators may be citizens respected by all sides, or professional diplomats, or religious or some other kind of leader accepted as fair. 
- Peace building, also called nation building. One description calls it "the process of normalizing relations and reconciling differences between all the citizens of the warring factions." Thomas Barnett calls it the system administrator, in his paradigm that failing states are disconnected from the "connected core" of developed nations. This often involves multinational ranging from demining to debt relief to preventive medicine.
Among other provisions, the Charter contains two important sections to help its members "maintain international peace and security." Although the Charter never uses the word, the generic term for these measures is peacekeeping, the kinds of observer or truce supervisory missions that occurred after a conflict, when combatants wanted to have the benefit of a trusted third party to act as a buffer. Traditionally, these missions have been known as "Chapter VI actions," because that section of the Charter deals with the peaceful settlement of international disputes.
However, Chapter VII contains the term peace enforcement, referring to military intervention authorized by the U.N. Security Council— blockades, enforcement of sanctions, forceful disarmament, and direct military action. These categories haven't always fit situations that seemed to go beyond peacekeeping but stopped short of actual combat, so an informal term, "Chapter Six-and-a-Half," emerged to describe such activities as conflict prevention, demobilization, cantonment of weapons, and actions taken to guarantee freedom of movement within a country. Mostly because of Cold War rivalries, only 13 U.N. peacekeeping operations were approved between 1945 and 1987. With the winding down of the Cold War, however, 13 new ones (not including the peace enforcement operation in Somalia) were approved between 1987 and 1992. There is another important figure that will come as no surprise to anyone who has ever stepped in to break up a barracks fight—during this same time, more than 800 peacekeepers from 43 countries have been killed while serving under the U.N. flag.
Consistency of objective
The disastrous operations in Somalia started as a well-intentioned humanitarian relief effort, but, without carefully redefining the operational requirements, suffered "mission creep", also called "strategic overreach".  The mission gradually became nation building, but without a consensus among various groups, who were quite prepared to respond with military force. 
The United Nations Secretary General defines peacekeeping as "the deployment of a United Nations presence in the field, hitherto with the consent of all the parties concerned involving UN military and/or police personnel and frequently civilians as well. Peacekeeping is a technique that expands the possibility for both the prevention of conflict and the making of peace."
Peacekeeping must always support diplomacy. Its military compnent may include:
- Withdrawals and Disengagements
- Prisoner-of-War Exchanges
- Arms Control
- Demilitarization and Demobilization
United Nations peacekeeping forces are invited by all sides, are multinational, and arrive after the fighting has ended... In the past, traditional peacekeeping was feasible because two conditions existed before peacekeepers were inserted: fighting had ceased, and both or all parties preferred the presence of the peacekeepers to their absence.
"Peacemaking...combines negotiation with nonmilitary tools of coercion to achieve a resolution of a conflict. When these tools are inadequate, military tools may be used to establish and maintain, forcibly if necessary, a cessation of hostilities. ... peacemaking constitutes the political framework for application of military force. Without a peacemaking effort, peacekeeping and peace enforcement operations will always fail.
"Even if military force is authorized by the United Nations, all military operations involve continuous negotiation, with all parties, and at many different levels." 
- Chairman of the Joint Chiefs of Staff (17 October 2007), Joint Publication 3-07.3, Peace Operations
- Barnett, Thomas P.M. (2005). The Pentagon's New Map: The Pentagon's New Map: War and Peace in the Twenty-first Century. Berkley Trade. Barnett-2005.
- International Online Training Program On Intractable Conflict, Peacemaking, Conflict Research Consortium, University of Colorado, USA
- Allard, Kenneth (January 1995), Chapter I. The Operational Concept, Somalia Operations: Lessons Learned, U.S. National Defense University Press
- Iklé, Fred Charles (2005 revised edition), Every War Must End, Columbia University Press
- U.S. Army Center for Lessons Learned, Chapter 2, Peacekeeping, Operations other than War, vol. Volume IV, Peace Operations
- U.S. Army Center for Lessons Learned, Chapter 1, Peacemaking, Operations other than War, vol. Volume IV, Peace Operations