The underlying causes of a conflict are important because they make the conflict intense and keep it so. The causes are embedded in history; the resentments they spawn date from events that occurred decades or even centuries ago as in Rwanda, their origins may not even be remembered. Often, the differing historical narratives become a part of the conflict itself.
Those historical roots are often kept alive by people who want to keep the conflict itself alive. Politicians, for example, frequently magnify the importance of these historical animosities for their own gain. By playing to longstanding fears and resentments among their constituents, they can increase their own power and legitimacy.