You'd need to edit /History Rewritten/Assets/Python/CivilWar.py. Near the top there is a section that looks like this;
Setting all of those entries to 0 will prevent dissent accumulating and thus civil wars from ever happening. It won't disable mention of dissent from the UI though, nor will it rebalance everything else to account for its absence. In particular, the AI still assume it exists when selecting civics and and buildings.
PHP:
self.iStarvationDissent = 50 # Dissent change whenever a city starves
self.iHappyDissent = -5 # Dissent change per excess happiness in city
self.iUnhappyDissent = 15 # Dissent change per excess unhappiness in city
self.iHealthyDissent = -5 # Dissent change per excess health in city
self.iUnhealthyDissent = 15 # Dissent change per excess unhealthiness in city
self.iCultureLevelDissent = -20 # Dissent change per culture level of city
self.iEthnicDissent = -1 # Dissent change from each % of player culture in a city
self.iEspionageDissent = -1 # Dissent change from espionage generated by a city
self.iStateReligionDissent = -25 # Dissent change if city has state religion
self.iNoStateReligionDissent = 25 # Dissent change if city lacks state religion
self.iNonStateReligionDissent = 20 # Dissent change for each non-state religion in city
self.iGreatTempleDissentModifier = -25 # Percentage change in dissent per Great Temple for a specific religion
self.iShrineDissentModifier = -50 # Percentage change in dissent per Shrine for a specific religion
self.iCivicLow = 10
self.iCivicMedium = 15
self.iCivicHigh = 25Setting all of those entries to 0 will prevent dissent accumulating and thus civil wars from ever happening. It won't disable mention of dissent from the UI though, nor will it rebalance everything else to account for its absence. In particular, the AI still assume it exists when selecting civics and and buildings.
