Abstract: Though the Caledonian and Irish experiences are widely different, common features call for investigation. In both cases, the question of State allegiance remains a major issue, connected as it is with a colonial past, with cultural, linguistic identities and above all with the sense of belonging or not to one or the other nation. In both cases it is becoming a matter of emergency to find new compromises, in New Caledonia in the wake of the referenda on self-determination, and in Northern Ireland, as Brexit represents a threat to the whole process that led to peaceful politics.