Liberia is currently monitored by a U.N. Peacekeeping Force, which took over responsibilities (and indeed personnel) from ECOMIL, ECOWAS's largely Nigerian force. The U.N. Peacekeeping force in Liberia is slated to be the largest current force with 15,000 mandated by the Security Council (S/RES/1509 (2003)
The merits of peacekeeping and its effects are much debated. There is no specific reference in the UN Charter to peacekeeping; rather, later missions have been shaped by experiences encountered in earlier ones. The first mission was the UN Truce Supervision Organisation (UNTSO), which began in 1948 with the end of the British Mandate in Palestine Today, there are 15 UN missions on three continents. Jean Marie Guéhenno, "A plan to strengthen UN peacekeeping: Third World Conflicts," International Herald Tribune, Monday, April 19,2004, last visited April 26, 2004. (http://www.iht.com/articles/2004/04/19/edguehenno_ed2_.php) The UN website has a timeline of all its peacekeeping operations (http://www.un.org/Depts/dpko/dpko/timeline/).
A number of scholars argue, however, that, since the Cold War and perhaps again in the nineties, the nature and purpose of peacekeeping fundamentally changed.
For a good introduction into the changed character of peacekeeping over time, see "Hawks and Doves: Peacekeeping and Conflict Resolution" of the Berghof Handbook for Conflict Resolution (Berghof Research Center for Constructive Conflict Management) (http://www.berghof-handbook.net/uploads/download/hansen_etal_handbook.pdf)
Here in the US, the Clinton Administration faced a great deal of public criticism for its part in the Somalia expedition, where a more ambitious agenda, encouraged by an African UN Secretary General, Boutros Boutros-Ghali, was undertaken and 18 Army Rangers were killed. Part of the problem was that the operation was poorly explained and thereby poorly understood by the public and the Congress. See Peacekeeping and Policing in Somalia, Lynn Thomas and Steve Spataro, National Defence University, Chapter 6 of Policing the New World Disorder: Peace Operations and Public Security, edited by Robert B. Oakley, Michael J. Dziedzic and Eliot M. Goldberg. Online at http://www.ndu.edu/inss/books/books - 1998/Policing the New World Disorder - May 98/PNW.pdf
After the massacres in Rwanda and Srebrenica, and the challenges posed by other recent UN missions, Secretary-General Kofi Annan commissioned a panel to evaluate the international organization's peacekeeping system. The Brahimi Panel, named after the Assistant Secretary General in charge of special projects who led it, issued its report (http://www.un.org/peace/reports/peace_operations/) in August 2000. The report had far-ranging effects in policy-makers views on the proper role of and implementation of peace-keeping missions.
The United Nations Dag Hammerskold Library has produced an excellent guide to research on UN Peacekeeping (http://www.un.org/Depts/dhl/resguide/specpk.htm). More information from the originating organizations are available for UN Peacekeeping (http://www.un.org/Depts/dpko/dpko/) and ECOWAS peacekeeping (http://www.ecowas.int/)
Another ECOWAS peacekeeping operation denoted as ECOMOG was implemented in Liberia in an earlier stage of the conflict (1990-1998), prior to the election of Charles Taylor. ECOMOG involvement has been both praised as a landmark development in regional peacekeeping and criticized as a force which took sides (based on Nigeria's major role and interests) and allowed the killing of President Samuel Doe in its presence. The online and print literature on this is voluminous: