Social movements usually have to do with change rather than persistence. And they usually emerge from "under-class" groups who lack meaningful access to other official and institutionalized means of power. They are among the "weapons of the weak", and their effectiveness usually turns on the ability of a sub-population to mobilize in collective action with determination and courage. Examples include the American Civil Rights movement, the use of strikes and boycotts by coal miners in the Ruhr after World War I, and the Solidarity Movement in Poland in the 1970s.
The question here is, what are the scope, limits, and mechanisms of social power wielded through social movements? Is it possible for a social movement to cause change in basic structures, policies, and distributions of wealth and power in society? (I am not thinking primarily here of revolutionary movements, but rather more prosaic struggles for improvement of some set of conditions for the under-group.)
The question arises because the terms of the problem essentially raise a social contradiction: a numerous but powerless group, advocating for a change of structure or distribution that harms the interests of the powerful, aligned against the most powerful forces in society. It would seem that this contest is inherently determined by the disproportion of powers held by the social actors. And yet we can provide memorable examples of success. So the question is, how does this work?
The first factor that provides an obvious source of potential power for the under-class group, is the size and functional role of the group in society. Several of the most obvious tactics for a social movement depend on this structural fact -- the strike, boycott, and mass demonstration. By mobilizing, the group can interfere with the smooth workings of society, compelling other parties to negotiate. And it can demonstrate its broad, mass-based support.
But the obstacles to these mass-based tactics are severe – classic collective action problems, problems of coordination and communication, and the need for competent organizations and leaders. And the tactics available to the powerful (the state, police, mine owners) are imposing: repression and intimidation, divide and conquer, co-optation, control of media, and a greater ability to wait out the struggle.
Besides mass mobilization, there is the tactic of broadening the movement through alliances. This strategy requires "changing consciousness" in the broader society by the actions of the under-class group. The group (primarily through its organizations and leaders) can strive to broaden the base of its movement through alliances with other like-minded groups and with the general public. And this depends upon successful communication -- setting the terms of the struggle in such a way that it aligns with the moral values and material interests of other groups.
Once again, the tactical options and advantages residing with the powerful are substantial. The powerful control the media; they have an advantage in setting the agenda; and they have an extensive ability to co-opt potential allies of the popular movement (side deals, special accommodations, playing off divisions within the mass population). But not all the face cards rest with the powerful.
So here we have several kinds of tactics for the social movement -- direct mass mobilization, broadening of alliances, and a deliberate campaign to capture the moral discourse for the public. But let's push forward and consider what comes next. Suppose there is a social constituency for an important structural change. Suppose this group is fairly strongly mobilized (in terms of the engagement of members), that it has competent organization and leadership, and that its members collectively play a significant role in the economy. Let us further suppose that the group has now engaged in all the tactics above -- large peaceful demonstrations in several cities, a few successful boycotts, and a successful communications campaign that has strengthened public support for the movement. Now what, in a constitutional democracy? (The analysis will look different within a dictatorship -- for example, the situation of labor unions in pre-war Nazi Germany).
It isn't implausible to conjecture that this scenario results in legislative action in support of the program. The public visibility and popularity of the struggle seem to lead to the inference that voters care about the issue, and legislators listen. So the social movement has won the day and has secured its objective. It has won the battle. But has it won the war -- is the change of policy a genuine and enduring change of structure in favor of the under-class? And here we can speculate again: the long, slow "tectonics" of power and privilege will turn back these gains in the future. The popular coalition cannot sustain its vigilance and mobilization forever; whereas the interests and strategic advantages of the powerful persist like great tectonic plates.
So on this line of thought, we can come to a provisional assessment of the causal powers of social movements in democracies: they have a fighting chance of securing tactical victories, but the prospects for achieving enduring structural change seem more remote. Their ability to change the rules of the game in a sustainable way seems limited in the face of entrenched and enduring interests opposed to such a change.
(Perhaps the Civil Rights movement is the rare exception to this statement. The rules of the game have plainly changed since 1953 with respect to race relations in the US -- in spite of the pressing need for further transformation.)
(There is of course a huge literature on social movements. A few interesting sources are Charles Tilly, Social Movements, 1768-2004, Gary Marx and Douglas McAdam, Collective Behavior And Social Movements: Process and Structure, Peter Ackerman, Strategic Nonviolent Conflict: The Dynamics of People Power in the Twentieth Century, and James Scott, Weapons of the Weak: Everyday Forms of Peasant Resistance.)