Reciprocity in the War against Terrorism?

Reciprocity is an accepted aspect of the laws of treaties and a recognized element of state responsibility. “No state is obliged by customary international law to remain passive when another state takes action inimical to its legally protected interests.” Countermeasures are likewise a recognized act of enforcement in international law, and the International Law Commission draft on the subject reads: “The wrongfulness of an act of a State not in conformity with an international obligation towards another State is precluded if and to the extent that the act constitutes a countermeasure taken against the latter State.” A material breach of a treaty by one party even enables the other party to “invoke it as a ground for suspending the operation of the treaty in whole or in part.”