The civil war (CW) duration literature sometimes finds that authoritarianism leads to shorter wars, and sometimes that regime type has no significant impact. Most commonly, authoritarian regimes (ARs) are expected to fight wars more effectively, thus ending wars earlier by military victory; but also to be more tolerant of war costs, and thus less likely to negotiate ends to wars. We also investigate whether ARs’ willingness to make substantive concessions to rebels – due to their lesser accountability – makes war-ending negotiations more likely. For theoretical and empirical reasons, we limit our universe of cases to the ethno-territorial type of CW and control for the effect of leadership preferences. Our results show that highly ARs tend to have shorter ethno-territorial wars and democracies longer ones; and that the concessions-constraint mechanism is the strongest and the war-costs-tolerance mechanism the weakest.