I think that both of your examples only worked because there was a contemporary, more militant version of the same movement, and the peaceful protestors were seen as a more palatable alternative.
As police and military units cracked down on militant revolutionaries/protestors, the people remaining in those movements moved toward more non-violent methods just as mainstream perception grew to see non-violent protest as more reasonable.
So the non-violent movement was pivotal in both cases, but I didn't think non-violent protest accomplishes either goal on its own.