ABSTRACT

Collective self-defence was unknown to traditional international law, despite the long-standing existence of treaty-based defensive alliances before the Second World War. However, collective self-defence may also arise spontaneously, without prior organisation. As said above, a treaty is not necessary for using the right of collective self-defence under international law, but it adds to the right a certain duty of collective self-defence. Traditional collective self-defence as formulated in Art. 51 UN Charter centred on the situation of an attack on the territory of a State. In terms of terminology it must be noted that, in the TEU, collective self-defence is called 'common defence'. Under the TEU, collective self-defence does not exist in the EU, It is a distant future possibility mentioned in Art. Inofficially, 'mutual defence' is more often employed. The important deterrent function of collective self-defence is thus little diminished.