I live in the ‘City of International Peace and Justice’ according to the city marketing of the municipality of The Hague. There is some truth in it, as the International Court of Justice, the International Criminal Court and temporary courts such as the International Criminal Tribunal for the former Yugoslavia are all located within the city limits. Yet the supposed relation between peace and justice is of course non-sensical. These international legal institutions may sometimes foster individual and sometimes even county-level justice, yet they have nothing to do with peace. History shows that punishing one war criminal does not prevent others to commit crimes against humanity, and settling a border dispute between two countries does not external effects elsewhere.
This is no surprise to classical liberals, as it confirms to their view on human nature, where emotions ultimately master rationality. This ensures international conflict and war are and will always be a feature in world politics. The most relevant question in international relations is not ‘how can we get rid of international violence and create a peaceful world’, but ‘how can we deal with the inevitable conflict that will be present?’. Perpetual peace is not attainable, perpetual war the norm, although luckily not of all people against all, all of the time. The value of international law is that it is one of the instruments that may channel or once in a while even prevent international conflict.
From a classical liberal perspective, international law is an expression of the common norms in the society of states, although without ultimate arbiter. Like law in domestic politics, international law must be restricted to the protection of the individual natural rights. And as in domestic politics, this has not been the case. International law has also exploded, while in many instances international law takes precedence in domestic legal order, which makes it even more important to limit its expansion.
For example, already Mises and Hayek objected to the explosion of positive international law, including the related establishment of international governmental organizations that occurred from the late nineteenth century onward. For classical liberals most international organizations, often created by governments of non-liberal persuasion, are attempts at constructivism at the international level. Mises and Hayek were also among the first to warn against the extended number of tasks of the League of Nations and both rejected the way the United Nations was set up. Hayek in particular warned against the inclusion of social and economic rights in the Universal Declaration on Human Rights and was very critical of the International Labor Organization.
Consequently, classical liberals should favor the abolition of international governmental organizations with tasks that extend beyond the principles of the limited state, spontaneous order, and the protection of individual natural rights. This is not a call for isolationism as there is also common sense in some international state cooperation and sometimes even a need for an international bureaucracy. I propose as a rule of thumb: if there is no need for state interference domestically, there is no need for international state action either. The exceptions are some tasks that follow specifically from international circumstances. Without going into details, this principle may, for example, lead to classical liberal support for aforementioned International Criminal Court and the special UN war tribunals, as the best way to punish people who infringed natural rights. But it may also call for the abolition of organizations that interfere with free markets and capitalism, such as the World Bank, the ILO, and the International Monetary Fund.
In short: some international law is beneficial, but most constitutes unwanted international constructivism.