International Law
Jan Klabbers
Second Edition
Summary of chapters: 1, 2, 3, 4, 5, 7, 9, 10, 13, and 16
Summary author: Nienke Cornelissen
Chapter 1: The Setting of International Law ........................................................................................2
Chapter 2: The Making of International Law ........................................................................................3
Chapter 3: The Law of Treaties ............................................................................................................4
Chapter 4: The Subjects of International Law ......................................................................................6
Chapter 5: Jurisdiction, Powers, and Immunities .................................................................................9
Chapter 7: The Law of Responsibility ................................................................................................. 10
Chapter 9: Sanctions, Countermeasures, and Collective Security ....................................................... 12
Chapter 10: Use of Force ................................................................................................................... 13
Chapter 13: The Seas, the Air, and Outer Space................................................................................. 15
Chapter 16: Domestic Courts and their Relationship with International Law ..................................... 18
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,Chapter 1: The Setting of International Law
As the ancient Romans knew, wherever there is a society, there will be law (ubi societas, ibi just), and
the rules regulating contacts within the society of states are generally called international law. This
book is dedicated to the study of public international law, as opposed to private international law.
Whatever the lawyer does, whatever the lawyer writes, and whatever the lawyer thinks will in some
way be based on an underlying set of ideas and assumptions about what the function of international
law is, and what role it should play. International law, in other words, can therefore not be portrayed
as politically innocent.
The history of modern international law is usually said to have started in the seventeenth century, with
the Peace of Westphalia in 1648. Europe would be divided into a numbers of territorial units, and each
of these units could decide for itself which religion to adopt (cuius regio eius religio). It was the creation
of sovereign states and, therewith, the birth of the modern state system. The second important event
in the seventeenth century was the publication in 1625 of Hugo Grotius’ On the Law of War and Peace,
describing the notion that all peoples have a right to trade, stating that trading routes, such as the
seas, ought to be free. Grotius forms a bridge between the classic naturalist way of looking at law (law
is not made, but found) and later positivist theorizing (law is not given, but man-made).
It is no exaggeration to state that international law has been closely connected with imperialism and
colonialism. Among the rules that allowed freedom of discovery and trade was the rule that territories
found overseas were to be regarded as not having been subject to sovereignty – as territory belonging
to no one (terra nullius). At the start of the sixteenth century, much of the globe became the
playground of the European powers, and at some point, the non-European world was literally divided
between two of them: Spain and Portugal. Later, towards the end of the sixteenth century, England
and Holland emerged as maritime powers, breaking the trading monopolies of the Portuguese in the
Indian Ocean. Grotius, in 1602, argued that the high seas were not terra nullius, but rather terra
communis: common property, and thus not susceptible to occupation and sovereignty.
International law also played a marked role when it came to slavery, first by allowing and organizing
it, and, later, in the course of the nineteenth century, by gradually arriving at a prohibition. Ironically
perhaps, international law is also still trying to come to terms with the effects of decolonization.
Much of international law is related to the economy; international law is the legal system regulating
the global economy, in much the same way as it has been observed that domestic legal systems and
law school curricula (at least in the Western world) from the late nineteenth century onwards were
set up so as to facilitate the capitalist economy. Over recent decades, international aw as also come to
embrace a version of criminal law.
The absence of a single overarching authority is perhaps the most noteworthy characteristic of
international law. How does international law function then? Various explanations are given, including
the fact that since states themselves make international law, they have little incentive to break it.
Another explanation is bureaucratic inertia, as well as reciprocity and the role of legitimacy. Finally,
states are few in number and are attached to their territories. They cannot escape easily.
The popular notion that international law is a system without sanctions is, at best, only partly true. A
practically relevant method of expressing dismay with another state’s actions is the so-called retorsion.
An important related mechanism is well known from domestic contract law; if A violates a treaty, then
B may do the same: inadimplenti non est adimplendum.
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, International law is in actual fact constantly in search of a compromise between the naturalist and the
positivist traditions. Also, international law is eventually the continuation of politics. What then
matters are the precise rules and principles of international law and the identity and mindset of the
people taking decisions, and the conditions under which the political debate can take place.
Whether or not one thinks that international law is useful often depends on the view one has of
international politics generally, and it is common to distinguish three approaches. First, self-proclaimed
realists tend to view international law as largely irrelevant. Second, liberal institutionalists think that
international law can be of relevance, at least if properly designed to take states’ lust for power into
account. Thirdly, according to constructivists, international law delivers the framework and vocabulary
that helps make international politics possible.
The emergence of globalization towards the end of the twentieth century has only strengthened the
connection between law and economics. If international law wants to continue to have something
meaningful to say about the conduct of international politics, if will need to adapt itself to the changing
world. To some extent, that process is going on as we speak.
It is not so much the case that international law is devoid of ethics, but rather that ethics itself is far
from uniform: different ethicists follow different traditions and present different conclusions as to
what exactly constitutes proper ethical behavior, or whose behavior counts, ethically speaking.
Chapter 2: The Making of International Law
In the famous Lotus case, the Court laid down the idea of international law as a permissive system;
behavior must be considered permitted unless and until it is prohibited. The two cases Lotus and
Wimbledon, together establish that in a horizontal order of sovereign equals international law is by no
means impossible. It is precisely because states are sovereign that they can make international law.
Some rules are so important that they also exist without consensual foundations. Such rules are known
as jus cogens rules: peremptory rules from which no derogations are permitted, and examples often
mentioned include the prohibitions of genocide, torture, slavery, and aggression.
Article 38(1) ICJ Statute provides information on the sources of international law. The most important
sources of international law are treaties and customary law, followed by general principles of law and
judicial decisions.
Rules have developed on the conclusion of treaties, the effects and application of treaties, their
validity, and their termination. These rules have been codified in the 1969 Vienna Convention on the
Law of Treaties (VCLT), which applies to treaties concluded between states only. A later Vienna
Convention was concluded (in 1986) to address treaties concluded with or between international
organizations, but this has yet to enter into force. For more on treaties, see Chapter 3.
In international law, customary law has traditionally played a very important role, and continues to do
so. Customary law has the advantage that precisely because it is based on social practices, it is usually
deeply engrained in the everyday life of a society. Article 38 ICJ Statute defines the requirements of
customary law as, first, the presence of evidence of a general practice. Secondly, the general practice
must be accompanied by opinio juris, a sense of legal obligation, or ‘accepted by law’.
The formation of a customary law takes state practice. However, what constitutes state practice is
debatable. In short, the evidences of custom are, and will remain, controversial. The requirement of
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