Terrorismo y secesion

Why does secessionism commonly involve terrorism? Two kinds of secession are distinguished, governmental and national. The former typically involves an attempt to gain a separate government to prevent oppression. It can, therefore, be a just war, but it is treated by the state as crime. As war and crime, it is argued, it counts as terrorism. The latter involves a claim to national government. It is for the same reason often terroristic, but can it be just war? A communitarian argument that it can be is presented.