The main aim of this book is to inquire into the system of norms regulating the `internationalization' of internal conflicts. The traditional distinction between international and internal conflict, which entails different legal consequences, is in practice very difficult to detect due to the presence, in many instances, of elements typical of both situations. Through a careful and extraordinarily useful examination of all relevant cases of `internationalized' internal conflict since 1956, the validity of the traditional framework of rules concerning foreign intervention in internal conflict is reassessed. At the same time, the applicability to these situations of the rules typical of international conflicts are analyzed with a view to providing the existence of a continuum between the two situations, not only as a matter of fact but also with respect to their legal regulation.