This chapter examines the place of international law in international politics, with particular emphasis on whether legal constraint is effective in averting or limiting the use of force by states. It begins with a discussion of the efficacy of international law in regulating the behaviour of states, focusing on the so-called perception–reality gap in international law. It then considers various reasons why states obey the law, from fear of coercion to self-interest and perceptions of legitimacy. It also explores the role and status of breaches of international law in international politics as well as the functions of the two laws of armed conflict, namely, jus ad bellum and jus in bello. Finally, it analyses the apparent paradox of legal constraint on warfare in relation to power politics and the mitigatory effects of norms governing the conduct of war.
