Why was the tactic of nonviolence so successful in achieving change?

The tactic of nonviolence has been used to achieve change around the world. Activists employing the tactic of nonviolence often use numerous means to reach their ends. They are known to organize mass noncooperation, economic boycotts, and civil disobedience, among other tools of non-violent action. Such actions have been shown to be successful when the activists engage long enough. Mahatma Gandhi and the nonviolence movement in India demonstrated that it was possible to succeed over a violent oppressor without the use of violence. The same was also demonstrated by Rev. Martin Luther King, as well as with other nonviolent activists during the American Civil Rights struggle.
Success for nonviolence is based on the fact that the tactic draws a clear line between the oppressor and the oppressed. The tactic identifies the victim by presenting their issues and forces the general population to side with the oppressed against their oppressors. The oppressors will characteristically continue pursuing a violent path, which will earn the oppressed support and sympathy. In the end, the oppressors are overpowered by the sheer number of the oppressed and their sympathizers.
http://www.bbc.co.uk/ethics/war/against/nonviolence.shtml

http://www.mshistorynow.mdah.ms.gov/articles/62/the-civil-rights-movement-in-mississippi-on-violence-and-nonviolence