Instead of letting the population divide along the guerillas' preferred lines of cleavage, based on sociological categories (race, class). They start out not remotely speaking for such large categories, merely thinking in terms of them. They try to force everyone else to think in terms of them, alone, by trying to make them the only relevant, life or death political matters. If they succeed in that, then they get whole huge categories of supporters, and the exact fight they desired between them. They ride their role in creating the fight to leadership of one side of it.
Remember that a quarter of a million Arab officials were loyal to the end, but abandoned by the French. Nothing is more revealing than that Eh Bien, you shall suffer. That was not created by the FLN, it was there from the outset and the war merely revealed it, by making the opposite course expensive. The contempt the political leadership of France had for their loyal charges in Algeria was the crux of the issue, the prior political basis for their eventual abandonment.
Guerilla politics is a sort of moral ju-jitsu of evil. It makes use of the worst aspects of its adversary - his bigotry, his extremism, his indifference, his duplicity. Those doing the using are far, far worse, of course. They are conscious moral corrupters for ulterior ends. But their targets are not angels, and that is half of why it worked. Naivete is not an answer either, as though childlike simplicity and kindness would be invunerable to such methods.
I guess what I am trying to say is that it is not simply a matter of nasty people knowing a nasty political technique. They put moral (and intellectual, but primarily moral) strains on their adversaries. Those adversaries bear some of the responsibility for how they react to the test that sets up.
Theologically speaking, devils tempt but sinners fall.