The previous chapter described the extent of a state’s physical territory; this chapter looks at how far a state’s legal power extends. As will be seen, international law places certain limits on the right of a state to make, apply and enforce its laws – its jurisdiction – and these limits are considered in Section 6.2. International law also recognises two principal bars to the exercise of that jurisdiction: diplomatic immunity and state immunity; these are covered in Sections 6.3 and 6.4. Two other bars to jurisdiction, namely special mission immunity and the foreign act of state doctrine, are also briefly covered in Sections 6.6 and 6.7.

This chapter covers the international law governing the use of force between states – the jus ad bellum. This is in contrast to the jus in bello – the law of armed conflict, or international humanitarian law – which regulates the conduct of hostilities once under way (see Chapter 11). Since at least 1945 the use of force by states has been prohibited, except in self-defence or when authorised by the United Nations Security Council. This chapter analyses the prohibition, the two exceptions, and the controversial issue of humanitarian intervention and its close relative, the ‘responsibility to protect’.

International economic law is an umbrella term with no fixed meaning. At its broadest, it covers all aspects of economic relations between states, including regulation of the conduct of individuals, corporations and international organisations. A narrower meaning is ‘the segment of public international law directly governing – rather than merely affecting – economic relations between States or international organizations’. The field also embraces governance arrangements, such as the World Bank, International Monetary Fund, and World Trade Organization, as well as the many UN and regional bodies that advance economic development. As space does not permit a discussion of all these aspects, this chapter focuses on two important areas: international trade law and international investment law. International trade law is the body of law, mainly treaty based, that governs the terms on which states permit the trade in goods and services across their borders.

Before the 20th century, most rules of international law were in the form of customary international law. Since then, the increased complexity of international relations and rapid international development have led to a substantial growth in the number and diversity of treaties. Article 38(1)(a) of the Statute of the International Court of Justice (‘ICJ Statute’) recognises treaties as a (material) source of international law by referring to ‘international conventions, whether general or particular, establishing rules expressly recognized by the contesting states’. Treaties now regulate trade, communications, environmental protection, military cooperation and defence, and human rights, to name but a few of the myriad topics. International environmental law, for example, is almost entirely governed by treaties, and international trade, investment and communications ‘are unimaginable without treaties’. The main rules in the law of treaties are contained in the 1969 Vienna Convention on the Law of Treaties (‘VCLT’), which governs treaty relations between states and is the focus of this chapter.