I think removing the current implementation of Anti-Warmonger Fervor without replacement would make attacking AI players too easy.
While the Vox Populi AI is playing very well for an AI it is still considerably worse than a human on the tactical level and needs some help.
After thinking about the problem for some time I came up with several approaches that I think could (at least in part) replace the current implementation of Anti-Warmonger Fervor:
==Option 1: Make Defensive Wars More Costly==
Currently defending against AI aggression does not really cost you much.
All you really have to do is gather enough Units at the border to kill the invading Units each turn.
As long as you are not losing Cities a defensive war does not really cost you much.
Basically the only cost you get is that your ability to trade is reduced.
However, if defending against AI aggression were to be more costly a warmongering player would face a much stiffer penalty for provoking all of his neighbors into attacking them.
There are several approaches by which this could be achieved:
The first approach would be to buff Pillaging and make the AI players aggressively harass their opponents when at war.
Basically the AI players would try to move a small number of Units around your main defensive line and try to capture your Workers and pillage your Improvements (especially Roads and Resources).
The rationale behind this tactic is that it would
- force their opponent to remove troops from the front line,
- inflict their opponents with extra Unhappiness, and
- reduce their opponents' ability to build Units and move them to the front line.
Pillaging tiles is a much easier objective than conquering Cities and I'm confident that the AI could be programmed to do it relatively well.
Even if the AI does not achieve optimal results when harassing their opponents they are probably going to achieve some results rather than none.
To make AI harassment more effective you could also buff Pillaging in some ways:
- Increase Gold reward for Pillaging.
- Increase Improvement repair times.
- Increase Unhappiness from pillaged Improvements.
- Give Pillaging a chance to reduce City population.
- Allow scouting Units and/or mounted Units to pillage at no movement cost.
- Allow naval Units to pillage adjacent Land Tiles.
- Allow Spies to spawn Barbarians.
- Remove attacks from Cities (but this has very far-reaching implications).
The second approach for making defensive wars more costly would be for attacks on Cities to cause permanent damage even if the City is not captured.
So when a City is damaged there could for instance be a chance that one of the Buildings is destroyed or that the City loses 1 Population.
==Option 2: Nerf Roads or Make the AI Use Them, Too==
Currently Roads are immensely useful for military purposes.
The default strategy is to basically put a Road onto every Tile on the border to an enemy player.
This gives all of your Units a huge mobility boost, allowing you to efficiently focus down enemy Units and easily swap out your own injured Units.
However, as of right now only human players seem to make good use of Roads.
Therefore, if Roads were to be nerfed this would make the game harder for human players.
Possible Approaches for nerfing Roads:
- Allow all Units to use Roads in enemy territory. This would make building Roads on all Tiles near the border a very risky strategy because it could allow enemy Units to penetrate deeply into your territory and possibly kill your valuable backline.
- Disallow Units from attacking and taking advantage of Roads on the same turn.
- Increase maintenance costs of roads (please don't, they're already extremely high in the early game).
As an alternative to nerfing roads you could simply make the AI use them, too.
In my experience it is extremely difficult to conquer Cities where the AI has built Roads for non-military purposes.
If the AI were to always build lots of Roads in their territory it would be much harder to invade them.
==Option 3: Nerf or Remove the Range Promotion==
Although it has been nerfed compared to vanilla Civ 5, the Range Promotion is still extremely powerful.
I would argue that it is single most important Promotion to use for both offense and defense as a human player.
The AI rarely ever gets to use the Range Promotion because it requires 100 Experience and their Units usually do not survive long enough to get it.
If the Range Promotion were to be nerfed or removed altogether it would make the game much harder for human players.
I think an appropriate nerf for the Range Promotion would be to change its effect to the following:
+1 Range. When attacking at maximum Range, deal 70% less damage.
==Option 4: Improve AI Usage of Bombers against Units==
I think the AI is currently not very good when it comes to using Bombers against Units.
If the AI were better at performing Air Sweeps and focusing down Units with the help of Bombers they would be much stronger in the late game I think.
==Option 5: Improve AI Naval Siege Capabilities==
I think the AI is currently still rather incompetent when it comes to naval sieges.
The AI seem to be rarely ever sending embarked land Units to go along with their naval Units and if they do they are not shielding them properly.
As a consequence you can easily take down the AIs' naval Units with just a few ranged land Units as long as you don't put them directly on the coast.
I think that if the AI were to embark several mounted Units and use them to threaten enemy ranged land Units their naval sieges would be more successful.
We talked about this in another thread with the idea of removing healing in enemy territory. What if we went further, and had units take damage in enemy territory based on war weariness? So the idea is that your supply lines start to exhaust and your units slowly weaken over long sieges. It hinders the human's ability to create a line and just slam a city until they win, they have to rotate in fresh units or risk their armies decaying to a point of easy kill. 
