Introduction

At the beginning of the 20th century and particularly during the era of the League of Nations, the freedom to resort to war became more and more restricted. The right of self-defence gained in significance, displacing the expansive right of selfpreservation. This development first culminated in the conclusion of the KelloggBriand Pact in 1928.1 The general prohibition of war laid down in Article I of the Pact was subject only to the reservation of the right of self-defence.2 Consequently, it was solely in the exercise of the right of self-defence that use of military force could still be lawful. The failure of the League to enforce the constraints on the waging of warfare, however, paved the way for sovereign excesses leading to the outbreak of World War II. The end of World War II saw the birth of the United Nations and another effort to put in place an international security regime to guarantee peace.