The crime of aggression is the criminalisation of the unlawful use of force. This is conduct that has a political dimension by definition and triggers sensitivity in the sense that even the slightest suggestion that the crime has been committed will be hotly debated and may lead to angry reactions. This will certainly be even more the case if it comes to an investigation or prosecution. It is therefore not an easy exercise to embark on writing a monograph on the crime of aggression. Very few books have been published on the extraordinary case of the crime of aggression, which is at the same time an international crime of particular relevance currently and one for which no prosecution has yet taken place. The crime was inserted into the Statute of the International Criminal Court in 2010.

The first edition of this book appeared in 2010 just before the Kampala review conference. The book was well received and frequently used. It played a role in the formulation of the definition of the crime. Gerhard Kemp now surprises the reader with a second edition. This second edition fully incorporates the results of the Kampala conference. It has kept the structure of the first edition to a large extent, but expanded on the newly inserted Articles 8bis, 15bis and 15ter ICC Statute. In addition, the author has included a new Part V on the national and regional prosecution of the crime of aggression. That chapter provides case studies of the two European states that have been the most active in applying universal jurisdiction: Spain and Belgium. These examples demonstrate how disputed the use of universal jurisdiction is. States that do prosecute international crimes do not receive only applause, but must anticipate damage to their international relations or even fear reprisals. As may be expected, this risk is even greater where one state passes judgment on the conduct of another in the crime of aggression.

Gerhard Kemp acknowledges this in Chapter VIII, Concluding remarks: “The complementarity imperative is supposed to make the application of international criminal law before domestic courts the default option of the international criminal justice project. The crime of aggression poses legal and political complexities that put it in a different category than the other core crimes.