The purpose of the jus ad bellum is to draw a line in the sand: thus far, but no further. In the light of modern warfare, a State should today have an explicitly recognized and undisputed right of delimited unilateral defense, not only in response to an occurring armed attack, but also in interception of an inevitable or imminent armed attack. This book, however, makes it evident that unilateral interception is not incontestably compatible with the modern right of self-defence in Article 51 of the UN Charter. Then again, unilateral defense need not forever be confined to self-defence only,...