WordNet (r) 3.0 (2006):

peacekeeping
    adj 1: of or relating to the preservation of peace between
           hostile groups by international military forces; "a
           peacekeeping force"
    n 1: the activity of keeping the peace by military forces
         (especially when international military forces enforce a
         truce between hostile groups or nations) [syn:
         peacekeeping, peacekeeping mission, peacekeeping
         operation]