Perhaps you are good to your neighbors, and the AI wants to show its gratitude? So it sends a herald, and gives you gold or tech or whatever. This is incentive to different methods of play- for example agreeable as compared to aggressive, and sets a precedent for ongoing good rapport and RELATIONSHIP development.
Also, something unexpected happens. A massive flood. A huge hurricane or earhquake. Or perhaps something less dramatic, but equally intriguing, like a messenger from a nation unknown and undiscovered and unanticipated. Perhaps the barbarians have developed a society.
Or, just something out of the ordinary. A magical and surreal barbarian class race, who, if you mess with them, curse your civ with horrible weather and just bad kharma generally, or if you are amiable it does the opposite.
Also, something unexpected happens. A massive flood. A huge hurricane or earhquake. Or perhaps something less dramatic, but equally intriguing, like a messenger from a nation unknown and undiscovered and unanticipated. Perhaps the barbarians have developed a society.
Or, just something out of the ordinary. A magical and surreal barbarian class race, who, if you mess with them, curse your civ with horrible weather and just bad kharma generally, or if you are amiable it does the opposite.