Self-Defense Against an Imminent or Actual Armed Attack By Nonstate Actors

There has been an ongoing debate over recent years about the scope of a state’s right of selfdefense against an imminent or actual armed attack by nonstate actors. The debate predates the Al Qaeda attacks against the World Trade Center and elsewhere in the United States on September 11,2001, but those events sharpened its focus and gave it greater operational urgency. While an important strand of the debate has taken place in academic journals and public forums, there has been another strand, largely away from the public gaze, within governments and between them, about what the appropriate principles are, and ought to be, in respect of such conduct. Insofar as these discussions have informed the practice of states and their appreciations of legality, they carry particular weight, being material both to the crystallization and development of customary international law and to the interpretation of treaties.