It is helpful when people make the necessary distinctions between the theology or philosophy of non-violence, and the use of non-violence as a political tactic.

The former, like liberation theology, seeks to establish a theoretical model to be used to fight oppression. The philosophies of well and little known champions of non-violence have often used in this way. There really hasn't been much incontrovertible "proof" that it has worked one way or the other.

The instances cited here as models of this philosphy (the partitioning of India/Pakistan, in El Salvador, and in the American South during the Civil Rights era) are examples of how people tried to implement the models in contexts of extreme violence. How effective the use of non-violence was in these instances is pretty controversial, despite the insistence of some true believers that non-violence "worked" in these situations.

The latter is a use of non-violence as a political tactic like any other. It is most often used only as long as it deemed effective in the context. This would include "sit-in" type demonstrations where people chain themselves to fences. The civil rights movement used it to great effect, but the anti-war movement of the 60s just never did seem to be able to get it together with this tactic. I would also add, the civil rights movement used it as a political tactic much more than it did as a philosophy of non-violence. The supposed non-violent philosophy of King has much more to do with his post-assasination legacy as embodied by his wife, than with what King actually believed in at the time.