An erga omnes obligation exists because of the universal and undeniable interest in the perpetuation of critical rights and the prevention of their breach.
Erga omnes obligations attach when there is a serious breach of peremptory norms of international law like those against piracy, genocide and wars of aggression.
In view of the importance of the rights involved, all States can be held to have a legal interest in their protection; they are obligations erga omnes.
[at 34] Such obligations derive, for example, in contemporary international law, from the outlawing of acts of aggression, and of genocide, as also from the principles and rules concerning the basic rights of the human person, including protection from slavery and racial discrimination.
The ILC refers directly in its comments to the article to the erga omnes principle and to the ICJ's acceptance of it in the Barcelona Traction case.