That is an easy one. Civil rights movement by itself would go nowhere, had it not been for the support of the fed, esp. the Eisenhower and the Kennedy administration. The US ruling class fell the heat of the Soviet competition - the Sputnik went up, the colonies were falling down (thanks to the Soviet support) so it was increasingly difficult for the US to cast itself as the leader of the free world and, at the same time, have the old slavocracy and lynching mobs practically running half of the country. The Southern racism, bigotry and anti-intellectualism became a serious liability to the imperial project and had to go, or rather be swept under the rug until they were resurrected by the Repugs after the Soviet "threat" subsided.
Do not get me wrong, I am not trying to discredit the sacrifices of thousands of courageous men and women who faced, often alone, the Southern rednecks and his elected officials. I think it was an act of extraordinary courage that I am not sure if I were able to muster. But the courage and sacrifice alone are not enough - they are important but they are not the sufficient and not even the necessary condition for a social change. The other crucial ingredient is a "window of opportunity" - i.e. the willingness of the ruling elite (or its part) to work with social movements. Absent that willingness (which itself may be cause by a crisis, a foreign threat, or internal competition with other power brokers), a social movement alone will almost certainly get nowhere.
Nor should it be construed that social movements do not matter - e.g. without the civil rights movement the changes proposed by the Eisenhower or Kennedy administrations would have probably been much more timid. I think the role of social movements can be compared to that of a fuse - they need a charge to cause an explosion, but without that charge they are just duds, fireworks, inconsequential bangs, sparks and smoke without fire.
However, that is often lost from the activists' perspective. Social movement participation has a profound effect on transforming one's cognitive frame - often leading to redefining the whole life of the activist and the whole world indeed in terms of goals and tactics of the movement. That often leads to loosing sight of a bigger picture. For one armed only with a hammer every problem looks like nail. These activists, or 'activistists" as our fearless moderator Doug dubbed them, become like little energizer bunnies, going and going and going and hoping in vain that playing their little drums will spark an avalanche - until they are run over by the wheels of history or their batteries run out of juice..
Wojtek