This paper offers a non-reductivist account of the requirement of legitimate authority in warfare. I first advance a distinction between private and public wars. A war is private where individuals defend their private rights with their private means. A war is public where it either aims to defend public rights or relies on public means. I argue that RLA applies to public war but not private war. A public war waged by a belligerent without legitimate authority involves a form of (...) illegitimate domination of the people. Contra the conventional wisdom that RLA is only an ad bellum principle, I show that RLA is also a vital in bello principle. Relying on the Kantian non-voluntarist account of political authority, I argue that only legitimate states have the right to wage public wars. However, I also contend that RLA is not an absolute requirement, even regarding the justice of public war. Under extremely unfavorable conditions, this requirement may be overridden by weighty considerations in favor of resorting to public war without legitimate authority. In sum, my account of RLA protects ordinary people from illegitimate coercion involved in guerrilla warfare in general yet generates proper permission for responsible, aspiring state founders to secure social justice by coercive means under extraordinary situations. (shrink)