In accordance with international humanitarian law, wars of national liberation have been expressly embraced, through the adoption of Additional Protocol I to the Geneva Conventions of 1949 (pdf), as a protected and essential right of occupied people everywhere.
Finding evolving vitality in humanitarian law, for decades the General Assembly of the United Nations (UNGA) - once described as the collective conscience of the world - has noted the right of peoples to self-determination, independence and human rights.  
Indeed, as early as 1974, resolution 3314 of the UNGA prohibited states from "any military occupation, however temporary".