in an ideal world non violence would be more effective, but theres only so far that can get you. atleast with violence people take notice quicker. but looking back over history violence has gotten more results. to quote mao zedong, "all power grows out of the barrel of the gun". examples of resolution sort by violence include, french revolution, american revolution, russian bolshevic revolution, spanish civil war, prussian formation of the germanic states, vietnam / indochina conflict, the list goes on forever. there are some examples of non violent ressolution such as ghandi and india and nelson mandela in south afrcia and the english revolution in the 1600's, but in these examples less of a change was won rather than complete change as with the violent ressolutions.
not that im all for violent resolutions, but it seems to bring faster an more effective results. which is why the examples of ghandi (who sort teachings from mandela) and mandela are such rare and great men in history.
dont know all that much bout mandela so i wont try to go into details, but i hope that helps with your non violence vs violence debate.