In February 1992, MacKenzie was named chief of staff of the United Nations peacekeeping force in former Yugoslavia, tasked with supervising the cease-fire in Croatia. The force headquarters were located in Sarajevo, the capital of Bosnia and Herzegovina. In April 1992 the Bosnian war broke out. MacKenzie created and assumed command of the peacekeeping force's Sector Sarajevo in May 1992. He used his UN force to open Sarajevo Airport for the delivery of humanitarian aid. Using the media as a means of trying to help restore peace, MacKenzie became an international celebrity.