The most effective action both resorts to power and engages conscience. Nonviolence does not have to beg others to ‘be nice’. It can in effect force them to consult their consciences - or to pretend to have them.
Nor does it petition those in power to do something about a situation. It can face the authorities with a new fact and say: Accept this new situation which we have created.
If greater gains have not been won by nonviolent action it is because most of those trying it…