(1) To soothe anger or agitation. (2) To subdue by armed action.
Example:
It took the police hours to pacify the angry demonstrators.
Unhappy babies are often given a rubber device for sucking called a pacifier to make them stop crying. In the same way, someone stirred up by anger or some other strong emotion can usually be pacified by resolving or removing its causes. In a usage that became popular during the Vietnam War, pacification of an area means using armed force to neutralize the enemy there and to quiet the local people who may have been supporting them.