Social conflict arises when structural change has not been possible, social conflict makes structural change necessary. Basically social conflict is rooted in inequalities between groups, though it is linked to social justice, the extreme form is that a group does not find the means to survive without structural change. The basic model (which has to be modified and adopted nowadays) is Karl Marx's theory of social classes.
Structural conflict? It is a serious social unrest that forces the existing system to radically change or modify to accommodate the alienated and dissatisfied ones!