Quests
It can be quite easy to lose motivation in the middle of a nearly thousand-turn long Civ campaign, with nothing much happening and success later on in the game being the only incentive to keep going. Quests seem like they could not only help with that, but also both tell and create more of a story. Quests are optional missions that players can take on, and which quests the player chooses and what choices they make during them will give the player points with certain affinities and determine what other quests will be available later on. In earlier games city states could give out missions that upon completion would improve the player’s standing with them, and the quest system seems to be the natural evolvement of this.