If you're talking about the American civil rights movement a good example is the non-violent tactics MLK employed (which are ideas he took from Ghandi). The peaceful march through Selma, Alabama highlighted the oppressive violence of the Jim Crowe south as the peaceful protesters were beat by state police without provocation. The images were aired on national news and were shocking to people of all colors throughout the rest of the country. These images and peace protesting baiting out violence were wildly effective in turning public opinion in favor of passing the Civil Rights Act of 1964.
