While it is vital to ask how state armies should wage just war against guerrillas, it is equally important to ask whether guerrillas and the people they claim to represent can wage just war against states. It is often thought that they cannot, that guerrilla armies systematically violate the principles of just war and leave state armies to wring their hands in frustration. If this dismal perspective dominates the thinking of state governments, it is decidedly narrow and, ultimately, unconvincing. Some, though not all, guerrilla organizations enjoy the right to press their claims by force of arms. To establish their right to fight, guerrillas must meet two challenges. First, they must show just cause and establish legitimate authority; second, they must fight justly. The first challenge is the subject of this chapter; the second challenge is explored in the following chapter.

Just cause reaches beyond traditional notions of territorial self-defense and affords some insurgents the right to use armed force as they strive for national self-determination. Similarly, the principle of legitimate authority – who, exactly, may authorize the use of armed force – broadens in the context of guerrilla warfare to include liberation movements and guerrilla organizations. Not everyone with a political grievance can pick up a gun and fight. Absent just cause and legitimate authority, guerrilla organizations indeed face charges of criminal behavior. Armed with just cause and legitimate authority, these same organizations enjoy the right to fight, the right to shed their uniforms, the right to combatant status, and, in some cases, the right to aid from the international community.