This article explains how foreign assistance to one or both sides in a civil war influences the dynamics of the conflict. It submits that external assistance has the potential of affecting the military capabilities available to the belligerents. It then argues that the balance of those capabilities impacts significantly on whether the warfare in a civil war assumes a conventional, guerrilla or irregular form. These theoretical assertions are tested against the case of the Angolan Civil War. It is shown that during that war, variations in the form of warfare correlated closely to the type, degree, and direction of foreign intervention given to each of the belligerents.