1. The Law of Nations or the Principles of Natural Law;Vattel Emer De;The Morality of War: Classical and Contemporary Readings,2006
2. Just War and Human Rights;David Luban;The Morality of War: Classical and Contemporary Readings,2006
3. comprising American leftists who went to fight for the Republicans in the Spanish Civil War, comes to mind; however, these troops were coordinated by the Spanish government, and more probably thought of as a foreign legion than a truly private force;The Abraham Lincoln Brigade;Spartacus Educational,2013
4. Is This War [in Kosovo] Good? An Ethical Commentary;Georg Meggle;The Morality of War: Classical and Contemporary Readings,2006