Consequences for Third States as a Result of an Unlawful Use of Force

Different sets of legal rules concur to define the legal position of third states in situations arising out of an unlawful use of force. Traditionally, the law of neutrality provided the main legal framework governing the question of the rights and duties of third states vis-à-vis the belligerent states.While the law of neutrality aims at the containment of the conflict and appears to be incompatible with the possibility of third party responses against an aggressor, with the crystallization of the rule prohibiting the use of force and the establishment by the UN Charter of a system of collective security, third states have been given the power, and under certain circumstances the duty, to react against an unlawful use of force.Lastly, a further development is the emergence of the category of obligations erga omnes and of a comprehensive set of rules establishing the consequences arising out of a breach of this category of obligations. The present paper aims at studying the interaction between these three sets of rules.