In simple terms, international law comprises a system of rules and principles that govern the international relations between sovereign states and other institutional subjects of international law such as the United Nations and the African Union (formerly the OAU). As we shall see, that is not to say that international law is unconcerned with the rights or obligations of the individual. Rather, it is that the rules of international law are created primarily by states, either for their own purposes or as a means of facilitating the functions of organisations of which they are members. Rules of international law cover almost every facet of inter-state activity. There are laws regulating the use of the sea, outer space and Antarctica. There are rules governing international telecommunications, postal services, the carriage of goods and passengers by air and the transfer of money. International law is a primary tool for the conduct of international trade. It is concerned with nationality, extradition, the use of armed force, human rights, protection of the environment and the security of nations. In short, there is very little that is done in the international arena that is not regulated by international law and it can now govern some aspects of relations between distinct units within a sovereign state, such as the territories of federal Canada or the devolved regions of the UK. International law is the vital mechanism without which an increasingly interdependent world could not function. In this sense, international law facilitates the functioning of the international community. However, that is not all. Modern international law also seeks to control states by inhibiting or directing their conduct both in their relations with other states (e.g. the law prohibiting the use of armed force to settle disputes) and in relation to individuals, both individuals of other states (e.g. issues concerning the exercise of criminal jurisdiction) and its own nationals (e.g. the law of human rights). It is the evolution of international law from a system that was concerned primarily with facilitating international co-operation among its subjects (states), to a system that is now much more engaged in the control of its subjects that is the pre-eminent feature of the history of international law in the last sixty years.
It is also important to realise that the practice of international law is intrinsically bound up with diplomacy, politics and the conduct of foreign relations. It is a fallacy to regard international law as the only facilitator or controller of state conduct. It cannot be this and, more significantly, it is not designed to do it. International law does not operate in a sterile environment and international legal rules may be just one of the factors which a state or government will consider before deciding whether to embark on a particular course of action. In fact, in many cases, legal considerations will prevail, but it is perfectly possible that a state may decide to forfeit legality in favour of self-interest, expediency or 'humanity', as with the Iraqi invasion of Kuwait in 1990 and the US-led invasion of Iraq some thirteen years later. There is nothing surprising in this and it is a feature of the behaviour of every legal person in every legal system, including that of the UK. If it were not so, there would be, for example, no theft and no murder. Indeed, in international society, where politics are so much a part of law, it may be that contextual and flexible rules, so evident in international law, are a strength rather than a weakness.
The nature of international law and the international system