This article aims to analyze the main lines of the evolution of the United Nations peacekeeping operations in the first fifty years 1946-1996 and discuss whether the use of force is compatible with these operations within the framework of a case study, namely UNPROFOR. The second generation operations which involved many new political and humanitarian functions, became more complex and multidimensional/multifunctional operations in contrast to the first generation peacekeeping operations. The use of force and the related problems are highlighted in the case of UNPROFOR.