This question originally appeared on Quora. 
Answer by John Prendergast, Activist. Author. Enough Project & Satellite Sentinel Project Co-Founder. Special Advisor - Not On Our Watch. http://www.enoughproject.org/
There is no single cause of conflict in the DRC. The conflict in Congo is a complex web of inter-connected needs, interests, and grievances that exist not only domestically in Congo, but also externally in neighboring states, such as Rwanda and Uganda, that have historically been involved in influencing Congolese politics, economics, and national security to protect their own perceived interests in the region.
The primary drivers of conflict in Congo can be broken down into three over-arching categories: political, economic, and military. Politically, conflict is driven for consolidation of political power that allows for access to state resources and revenues--usually for personal profit. This conflict is driven between groups with various political, tribal and/or ethnic affiliations and is played out at local and national levels. Economically, conflict is driven by the government, rebel groups, and external actors for control over Congo's vast natural resource wealth, including some of the worlds largest strategic mineral reserves. This conflict is played out primarily in Congo's eastern provinces and southern Katanga province. Militarily, conflict is driven due to the government's inability to extend complete control over its security services. Deep divisions within the military, as well as individual corruption and opportunism have created a national army that has been implicated in large-scale theft, extortion, human rights violations, and mutiny. This conflict is played out primarily in the east and in Kinshasa. As a sum of their parts, these various drivers of conflict have lead to chronic instability and conflict in Congo.