Asustained action taken by citizens disenchanted with government in order to express their opposition and work to bring about social or political change is a

Social movement

Explanation:

Social movement, refers to a group of people who form a sustained campaign that works towards achieving a common social goal. People come together because they can see something need to be changed or they are dissatisfied with what is happening in their society , therefore they want to engage in a movement that will bring about a change. These are people who are brought together because they share a common outlook on society and they work collectively on one goal.