In the post-Cold War era, the role played by standards or rules regulating conduct both between and among states and individuals has received increased scrutiny. This is due, at least in part, to the proliferation of such rules resulting from the end of the superpower conflict and generally higher levels of cooperation among states that have marked this period. At the same time, growing interdependence among states – especially in the economic sphere – as part of broader globalisation processes has enmeshed many states in a web of diverse obligations covering an ever-flourishing range of activity. Thus, today, as a result of its membership of various international organisations, a state may find itself simultaneously obliged by a European Union directive to change its own domestic social legislation, prevailed upon by NATO to provide military assistance to a peacekeeping mission, the subject of a trade ruling by the WTO and under pressure to comply with a ruling of the UN Human Rights Committee – to name but a few examples. While it is true that membership of such organisations is voluntary – and therefore, formally, states are free to withdraw from or reject membership – in practice rejection is more and more difficult as issue areas become increasingly interlinked. Consequently, burgeoning interdependence means relations between states become more frequent and sustained, and the number of occasions upon which, for instance, state A is prepared to accept political concessions in one area on the condition that state B accepts economic concessions in another, also grows. Where interdependence among states is both deep and wide, the follow-on costs of rejecting a particular obligation are likely to be higher. Like states, individuals have also found themselves subject to an expanding range of rules in recent years. While domestic standards for individual conduct are nothing new, these are now supplemented by a variety of regional and international rules. Thus, Europeans are bound by a whole host of EU technical standards governing areas such as construction, food supplements and health and safety. Under the ICC Statute, an individual may be prosecuted for genocide, war crimes and/or crimes against humanity where either their state of nationality or the state where the alleged crimes occurred is a state party to the Statute and is ‘unwilling or incapable genuinely to carry out the investigation or prosecution’.1 Even the highest national office-holders cannot automatically escape personal individual criminal responsibility: the House of Lords’ decision in Pinochet2

recognised that the principle of sovereign immunity is not without limits. The conduct of individuals as employees is also subject to constraint, as non-state actors such as corporations sign up to international standards regulating areas including financial reporting and labour conditions.3 Online interactions also bring individuals within the remit of foreign and international norms as never before. As a consequence, a growing number of individuals find themselves at the centre of diverse regimes of obligation, with little guidance on how to reconcile different obligations, and where reconciliation is not possible, which can and should take priority. This proliferation of obligations regulating the conduct of states and individuals has given rise to growing interest in the nature and locus of binding authority in international affairs. Drawing on the above examples, the pertinent questions thus become: What type of obligation (if any?) is being created when a corporation endorses a voluntary international standard, and how does this rule differ from a state’s obligation to contribute under the terms of a military alliance? Is the former a moral obligation only and the latter a political and legal obligation? Or does each type of obligation contain within it moral, political and legal elements? Most significantly, who has competence to decide these questions, and what are the distinctions between political, legal and moral obligations in terms of consequences? These questions of authority, or ultimate decision-making or enforcement power in international affairs, are at the heart of the debate between two schools of thought in particular: cosmopolitanism and communitarianism. Generally speaking, cosmopolitans argue that universal standards applicable to humankind should take priority in international affairs, and that examples such as the current inter national human rights regime demonstrate a move in that direction. By contrast, communitarians contend that the ‘community’ is the main source of obligations, and that a plurality of communities exist worldwide. The cosmopolitan-communitarian debate will be discussed in greater detail below; it suffices at this point simply to acknowledge that while rules for states and individuals have multiplied exponentially in the current era, fundamental questions about the rule-makers, the nature of the obligations that are created and the basis of rule-making authority remain. These key questions about rule-making in the international arena have emerged time and again in the context of efforts over the last ninety years to entrench and develop a rule prohibiting aggression. In order to achieve the goal of outlawing aggression, diplomats, lawyers and politicians alike have had to grapple first with the primary substantive issues raised by this concept – such as what aggression actually is, who is capable of committing it, and against whom it is committed. In the process of discussing these matters, however, secondary questions – including which body or bodies are the most appropriate for ruling that an aggression has occurred on a specific occasion, what the consequences of such a ruling are (related closely to the question of what the purpose of a rule banning aggression is), and the procedure for making such a ruling – have inevitably come to the fore. A reconsideration of the concept of aggression’s role in international relations can therefore be expected to shed fresh light on the current theoretical revival of these latter normative questions.