An Essential Function of International Law. "Professor Kelsen's high standing as a scholar is sufficient to commend in advance any volume that comes from his pen. But in this case he has chosen a subject that will at once challenge attention. The main function of the volume, in the words of the author, "is to show that collective security is an essential function of law," that it is "by its very nature a legal problem." A generation ago there were many in high places to contest the thesis. Today the bitter lesson of two world wars has established the principle for practical purposes, in spite of the difficulty of putting it into practice. But the legal aspects of the thesis remain to be clarified, and this is what Professor Kelsen does with all his power of legal analysis and systematic presentation. (...) [We] must be grateful for what we are given, an acute analysis of a fundamental principle, the applications of which we can make from our own knowledge of recent history." -- C. G. Fenwick, American Journal of International Law 52 (1958) 811. Possibly the most influential jurisprudent of the twentieth century, Hans Kelsen [1881-1973] was legal adviser to Austria's last emperor and its first republican government, the founder and permanent advisor of the Supreme Constitutional Court of Austria, and the author of Austria's Constitution, which was enacted in 1920, abolished during the Anschluss, and restored in 1945. He was the author of more than forty books on law and legal philosophy. Active as a teacher in Europe and the United States, he was Dean of the Law Faculty of the University of Vienna and taught at the universities of Cologne and Prague, the Institute of International Studies in Geneva, Harvard, Wellesley, the University of California at Berkeley, and the Naval War College.