A short study in the Rand manner (i.e., heavily taxonomic and tabular) on an important subject. Insurgency does not normally survive without some kind of external support. That lesson was made clear as early as the 1781 Battle of Yorktown, when the British general Charles Cornwallis saw French muskets and artillery pieces in the hands of American soldiers and ranks of French soldiers standing at a discreet distance. Here the authors make an important point: external support comes not only from states but increasingly from nonstate actors, particularly diasporas and substate organizations. These groups are initially less dangerous than states, but they are also less amenable to disruption or coercion, which augurs ill for the perpetuation of a peaceful status quo in many parts of the world.