The following is an excerpt from the Designer Notes for Old World. The game, a historical 4X set in classical antiquity, released on July 1, 2021, and is available for purchase here.
Some mistakes are inevitable because the idea behind them is so hard to resist. When tasked with improving diplomacy in Civ 3 – and not just in comparison to Civ 2 but to Alpha Centauri as well – the most obvious decision was to add a bargaining table, where players can customize their deals as much as desired. Instead of relying on the AI to suggest interesting deals, the player could pick and choose whatever they liked – gold and iron for a city, or a luxury for a technology, or some gold each turn for open borders and a map, or any other combination. It was one of the standout features of Civ 3 and became a standard feature of the 4X genre. Unfortunately, it was a big mistake.
The first issue that appeared was how quickly the AI traded technologies with each other. I had allowed the AI to trade techs freely because the human was now free to do so via the bargaining table. The problem was that unhindered tech trading will always be problematic because the player that “gives away” the tech is not really giving away anything. The only downside is that a rival is getting access to a tech, but the usual rationale is that if you don’t give the Babylonians Ironworking, then someone else will do so, and you’ll just miss out on whatever you would have gotten from them. Even worse, if you didn’t play the tech trading game, the AIs would make the trades anyway, and it would appear to the human like you were playing against a cartel of AIs that all seemed to be at the same tech level. According to the rules of the game, the AIs were just playing optimally; the problem was that the rules were bad.
With Civ 4, I made a number of changes to improve the bargaining table. Tech trading was severely limited by making the AI unwilling to trade techs with players they disliked (or even just didn’t like enough). They would also simply refuse to trade techs with players who were in the lead, and as these rules applied to humans and AIs equally, the worst excesses were avoided. The system also prevented trading lump-sum items for per-turn ones, so no more taking a giant loan from a neighbor and then declaring war to get out of the payments. Players could now ask the AI to fill in either side of a deal so that, in order to play optimally, you weren’t forced to add 1 gold to either side to see if the deal crossed the magic threshold.
However, the system was still fundamentally flawed because it gave the player too much control over diplomacy. The best strategy remained contacting the AIs as frequently as possible to extract whatever deal was most advantageous. Diplomacy did not feel like diplomacy; it felt like walking up to a vending machine and picking the option that suited you best. Players were ruining the game for themselves by playing optimally, however boring that might be. Diplomacy had become simply another part of your economy, a reliable source of gold or technology or resources, depending on what you needed. Ideally, diplomacy would be unpredictable at times, would be outside of the player’s control although still reactive to the game state, and would allow the player to be opportunistic but also force them to face difficult decisions.
Fortunately, Old World had a system in place that could do all of those things easily – namely, the event system, which is both inherently unpredictable yet also reactive to the current game state. The event system became more flexible and robust the longer we worked on it, and we already used it for both the tutorial system (teaching you about harvesting the first time your Scout steps onto a neutral resource) and the mission system (every assassination has a small chance of triggering an event which can spin the game off in unpredictable directions). Using events to manage all diplomatic interactions between the human and the AI was perhaps a risky decision – players had gotten so used to the bargaining table that leaving it out could come across as a step backwards – but it would make diplomacy more dynamic and also force us to expand the event system to include more diplomatic triggers, requirements, and effects, which could pay off in the long run for scenarios.
The first step was handling all diplomatic changes (war, truce, peace, alliance) via the mission system, which would then trigger an event when the mission was complete. Thus, the event system would need to know about the proximity of different nations, their relative strengths, and the current state of any war (who is winning and by how much). The event options would need to be able to set diplomatic states, handle trade and tribute, and add memories and relationships which modify opinions. Each of these elements might not have been part of the event system if it wasn’t responsible for diplomacy, but once they were added, they could be used for any event, making the whole system more varied and robust. Once all the diplomatic elements were in place, the event system could do all the work of a traditional 4X diplomatic system but with the upside of all the other features of events, such as testing to see if your spouse was from their nation or if you share a religion or if one of your cities used to belong to them.
Because diplomacy was now less predictable, it was important that the player couldn’t ask for something too frequently, or else the player would be encouraged to keep trying until they got the event they wanted (exchanging a vending machine for a slot machine). To avoid this problem, we gave diplomatic relations (such as asking for peace or a trade deal) a cost in Civics or Training, and we also limited diplomacy to missions that could be conducted by your Ambassador. Not only did this bring another character to the forefront, always a good thing in Old World, but it meant that only one diplomatic mission could be pursued at a time and, more importantly, that missions would take multiple years to produce a result. The latter was important so that players were not tempted to use the undo system to reverse unsuccessful diplomatic missions and maybe offer tribute to end a war instead (in other words, trying to protect the player from themselves). Of course, the most unpredictable aspect of diplomacy is if your ambassador dies in the middle of a mission (although we do warn players before they send a sick ambassador to ask for a truce).
I was actually expecting more pushback from players for the lack of a bargaining table (the inability to found cities anywhere has been more controversial), so I hope that players appreciate how much the event system makes diplomacy more dynamic and unpredictable. Unlike many other systems I’ve designed, the health of the diplomatic system rests not just on the quality of the underlying algorithms but on the simple quantity of diplomatic events our writers have created, and by this metric the system will only get better as our writers add new events with each weekly update.