1 Introduction

Before the two World Wars of the twentieth century, international law was a system essentially focused on sovereign states as its main founding elements. Thus, Ludwig Oppenheim stated in the first sentence of his well-known textbook that: Law of Nations or International Law (Droit des gens, Völkerrecht) is the name for the body of customary and conventional rules which are considered legally binding by civilised States in their intercourse with each other.1 That sentence was not only a technical description. It meant at the same time that the state stood at the...