John A. Warden's airpower theory, The Enemy as a System, has had a major influence on the strategic discourse ever since the foundation of this normative framework was presented in The Air Campaign in 1988. Warden’s theoretical impact was reinforced by the American successes during the Gulf War, but since then, little research has tested the theory outside the context of conventional wars of aggression. This study analyzes The Enemy as System against a peace enforcing context, characterized by multilateral cooperation. It also identifies intermediate variables that help explain why the theory is strengthened or weakened in relation to this particular context. Through qualitative methods, Operation Allied Force and Operation Unified Protector are analyzed against operational indicators within the central concepts of the five-ring model and parallel attacks. The results of the study show that NATO did not use airpower in accordance with Warden's normative theory in either of the examined operations. The absence of operational indicators could hypothetically explain why NATO failed to produce strategic effects within the operational time limits, although this remains a speculative conclusion. The result instead suggests a number of intermediate variables, such as political disagreement and strategic dissonance, which combined reduced the possibility of using airpower in accordance with Warden's theory. In addition, the fear of civilian casualties and the risk of exacerbating the post-war humanitarian situation, further reduced the possibility of attacking targets within certain subsystems of the five-ring model. The conclusion is therefore that Warden’s theoretical applicability, and thus universal validity, is weakened within the examined context.