Self-defence principle

Kretzmer 2013, p. 246 ( The view that an attack by non-state actors that is not imputable to a state cannot constitute an armed attack has been rejected by the vast majority of publicists... ). See also Greenwood 1989, p. 274 (who would extend the application of self-defence principles to operations such as protection of nationals abroad, humanitarian intervention and the protection of national vital national or international interests if they were viewed as occurring outside the context of self-defence). 

The principle of self-defence, allowing action to be taken against an actual or impending attack. 

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