I need to go to sleep, but I'll be back in a few days to post more info on the subject if you want to. Maybe some sources as well (if I have the time).

For the moment: The black civil rights movement was pretty much alive throughout the century and several internal conflicts erupted. In the 1930s, W.E.B. Dubois and Walter White had some disagreements over the aims of their struggle and how they could secure civil rights for Blacks. Dubois, a leading figure of the early movement and of the National Association for the Advancement of Colored People (NAACP), stepped out (or was kicked out) from numerous important positions in his gradual detachment from the Association, including Secretary of the Association and Editor of "The Crisis" (the official "journal" of the NAACP- published on a monthly basis)... Walter White, who was becoming more and more prominent in the NAACP and as a black leader in general took his place as Secretary of the Association disagreed strongly with Dubois' somewhat newfound "black nationalism" and on the objective of integrating Blacks in the American society. To keep it short: White believed in complete integration, while Dubois thought that creating a distinct society was the only remaining option to secure full civil rights for African-Americans. His departure from the association came in 1934 and started a "new era" in the history of the NAACP (although the integration goals were the NAACP's and Dubois' initial objectives as well) under the leadership of Walter White and Roy Wilkins.

Similar "nationalism vs. integrationnism" feud occured throughout the movement. During the 1920s, Marcus Garvey was a loud advocate of pan-africanism and reached plenty of Blacks with his "back-to-Africa" campaign, which was partly a fraud. A lot of intellectuals and civil rights activists from the Harlem Renaissance were inspired by African lore and traditions (especially among black artists), but the "back-to-Africa" movement was often severly criticized. Malcolm X's position is also one of black nationalism and was opposing the ideology of the mainstream movement (of which Martin Luther King is the most recognized leader).

Of course, these accounts are over-simplification of conflicts. The black civil rights movement was also crippled with other internal conflicts, but I really need to go to sleep, so I'll come back in a few days to give more details.

I don't know much about other civil rights movement, but I'm sure there are other historians that would be able to inform you on the question.

P.S.: to answer your question, the ideological difference between White and Dubois seems to have many origins. A quick list: Class: not so much Generational: after decades of work bearing little fruits, Dubois became disenchanted, cynical and dissilusionned (or so he thought) about the american society. White was younger and that might have played a great role in his optimistic stance. Educational: not so much. Racial: both were black, but White could pass for white... it might have played a role in their vision of integration as White could far more easily integrate a white audience.

If I did a similar exercice with the likes of Garvey, Malcolm X or Martin Luther King, I would get significantly different results. My guess is that those ideology were not confined to certain classes, sexes, races, etc. While they certainly were influenced by such divisions and by personal experience, I think that being a black nationalist had a lot to do with personal reasoning.

This is really interesting. I'm also curious about how this worked in the LGBT movement. I read somewhere the 1968's generation was much more radical towards deconstructing gender than interested in simply achieving homosexuals' inclusion in patryarchal society.