Operation Deny Flight was conducted from April 12, 1993 to Dec 20, 1995, when the international Implementation Force assumed responsibilities for the implementation of the military aspects of the Peace Agreement on Bosnia-Herzegovina. During nearly 1,000 days, NATO enforced a no-fly zone and effectively prevented the warring parties from using Bosnian air space and made a key contribution to the peace process.
Read this study, published in the Summer and Fall 1997 issues of Airpower Journal:
Balkans Air Campaign Study Part 1
Balkans Air Campaign Study Part 2