Go to MODS folder, (1)Community Patch, Core Files, Core Changes, and select DiploAIOptions.sql
-- [DISABLE ENDGAME AGGRESSION BOOST]
-- If set to 1, AI civilizations will not receive the large late-game aggression boost towards players that are close to victory.
-- Bonuses/penalties for general victory competition will continue to apply.
-- NOTE: If Victory Competition is disabled, this does nothing.
INSERT INTO Defines (Name, Value)
SELECT 'DIPLOAI_DISABLE_ENDGAME_AGGRESSION', '0';
Set this to 1. I'd also turn off War Bribes:
-- [DISABLE WAR BRIBES]
-- If set to 1, AI civilizations are unable to bribe other AI civilizations into declaring war, but they can still bribe (and be bribed) by humans.
-- If set to 2, the option to bribe another AI civilization into declaring war on a third party is removed globally.
-- War bribes between human players are unaffected by this setting.
INSERT INTO Defines (Name, Value)
SELECT 'DIPLOAI_DISABLE_WAR_BRIBES', '0';
Set this to either 1 or 2. Maybe even disable coop wars too!
-- [DISABLE COOP WAR REQUESTS]
-- If set to 1, AI civilizations will not request that friends join them in a cooperative war against other players.
-- This does not affect offers in the Trade screen to declare war on a third party.
-- Humans can still request that AI friends join them in a cooperative war.
INSERT INTO Defines (Name, Value)
SELECT 'DIPLOAI_DISABLE_COOP_WAR_REQUESTS', '0';
And actually if you do want to play a completely peaceful game there is also a setting in there for that too:
-- [PASSIVE MODE]
-- If set to 1, AI civilizations will never declare war on human players. They also won't attempt Domination Victories, unless they can win one without declaring war on a human.
-- If set to 2, AI civilizations will never declare war on any other civilizations or City-States. They also won't attempt Domination Victories, unless they can win one without declaring war.
-- Humans can still declare war on AI players, and AI players already at war will still fight their opponents.
INSERT INTO Defines (Name, Value)
SELECT 'DIPLOAI_PASSIVE_MODE', '0';