One of the big changes in Rising Tide was the replacement of the open ended trading between Civilizations with a much more constrained system involving a new resource called Diplomatic Capital. Open ended trading has existed since Civilization 3. While the trading system has changed over time (Technology Trading was replaced with Research Agreements in the move from Civilization 4 to Civilization 5) this represents a far more radical change. Despite the new system being controversial I believe it is a significant improvement that will be carried through to future games in the Civilization franchise.
It gives Civilizations a reason to Cooperate
Civilization is a zero-sum game. At the end there can be only one victor. Two Civilizations can be allies throughout the whole game but as victory approaches it makes sense for one ally to turn on the other and try to seize victory for themselves. This creates tension (or conflicting metaphor) when compared to how nations interact in reality. It is common for nations to develop and maintain cooperative alliances that last for generations. Nations are able to do this because they have an infinite time horizon. There is no victory condition that they are racing for that warps all their decision making.
This poses one of fundamental questions in strategy games. Should the AI try to mimic a human-player and play the victory condition? Or should the AI role-play even if that means it will passively sit there while an ally cruses to victory? There is no universal answer to this question. It depends on what style of game the designer wants to create. You can see Soren Johnson (the designer of Civilization 4) discuss this question in his talk Playing to Lose: AI and “Civilization”.
The new Diplomacy system in Rising Tide doesn’t resolve this question but it does lessen the tension. Forming agreements is valuable even if at a later point in the game you will need to race the other Civilization for victory. Long term alliances can form just because each participant wants to upgrade the effects of their agreements.
The AI couldn’t handle open ended trading
Open ended trading has been around since Civilization 3 and the AI has been bad at it the whole time. In Civilization 3 high difficulty AIs started with a Worker to help them develop faster. However, AIs would happily trade away their starting Worker to a human for a bit of Gold, even through a Worker at that stage of the game was hugely more useful than the Gold. In Civilization 5 humans would generate most of their Gold by trading away surplus copies of their Luxury Resources to AIs. AIs would be willing to take the Luxury Resources even though they had more Happiness than they could use.
Workers, Luxury Resources and Gold all have value. But getting the AI to correctly value those things based on what stage of the game it is in, what it needs, and what it is trying to do is extremely difficult and generally infeasible. If it makes a mistake anywhere players can usually force it to keep making that mistake over and over.
Rising Tide’s diplomatic system side steps this difficulty by preventing open ended trades from even being possible. This may seem overly harsh but when designing systems one of the constraints is “Can the AI understand it?”. If the AI can’t, then the system probably won’t work well.
Diplomacy is less of a Black Box
In previous versions of Civilization answering the question “Why won’t this Civilization ally with me?” required understanding the complex algorithms that governed AI behavior. To players who weren’t familiar with the code these algorithms were black boxes. A player may want to know why the AI isn’t accepting their alliance but that information is not visible in game.
Rising Tide’s diplomacy system makes the question easier to answer, “the player’s Fear or Respect isn’t high enough”. Fear and Respect are directly visible in game and players can watch them change over the course of the game as circumstances change. Messages at the top even draw attention to these changes so players can better understand what behaviors effect them. These changes make it possible for players to engage and understand the mechanics of diplomacy without having to dig through the code themselves.
Diplomacy is a continuation of war by other means
Diplomacy in Civilization games often revolves around controlling war. Avoiding wars with Civilizations you don’t want to fight and weakening Civilizations you do. Rising Tide’s diplomacy system does an admiral job over providing other considerations that add nuance to diplomacy. Managing agreements and their entanglement with alliances pushes players to act in ways that previous diplomatic systems did not. The need for resources may drive players into alliances instead of simply using open ended trades to fill in their needs. Lastly, the Fear and Respect system helps communicate to players how all the interconnected choices they are making feed into the eventual behavior of the AIs. There is tons of potential in this design and it will be interesting to see what future games in the franchise do with it.