The vassal system is still broken. But it can be fixed by making it simpler.

[Zoolooman]

Vassals are troublesome. The vassal system isn't complex enough to mimic the deliberations that ought to occur whenever one country becomes the vassal of another. This causes frustration when the player feels that the system has cheated him.

For a long time, I thought that the best solution was to increase the model's complexity to match what the player expected. This would give the player more choices and more diplomatic options.

But recently, it occurred to me that the problem with the vassal model is that it's too ambitious. Vassal behavior feels awkward because too much is allowed--even when common sense would dictate otherwise.

Hence, I've come up with a slightly simplified version of the current model. It fixes the common complaints while maintaining the game's current balance.

THE SIMPLE VASSALS MODEL

Capitulation

When the AI can capitulate: when it is at war.

To who the AI can capitulate: the enemy Civilization that it has been fighting the longest during this particular war.

Special cases: if a capitulating AI has vassals of its own, then when he capitulates, his vassals become vassals of the new master.

EDIT: An interesting alternative: if it can be reliably measured, the AI can only capitulate to the Civilization that has done it the most harm during the war.

Vassalization

When the AI can vassalize: anytime.

To who the AI can vassalize: if at peace, anyone it chooses; if at war, only to current war allies--vassalization cannot bring anyone new into a war.

Clarification: If an AI wants to become the vassal of another Civilization during a war, he must first bribe or ask that AI to join the war, and his offer must be made independently of his desire to become a vassal. In other words, the AI cannot offer their vassalage as part of the war-bribe bargain, and the AI should not take the value of a potential vassal into account while joining a war. This simplifies the AI's interaction with the vassal system, it prevents the suicidal wars that the AIs sometimes start through vassalage, and it also prevents Friendly civilizations from accidentally joining a war against a Friendly buddy.

Special cases: if an AI at peace vassalizes itself to a civilization in a war, then it gains the war status of its new master.

Exceptional case: An AI cannot vassalize himself to a master who is at war with someone that the AI has an unbreakable peace treaty with. For some reason, this is currently possible in BTS. :P

Vassal Behaviors

For all vassals

• Vassals cannot perform active espionage on the master or the other vassals of the master, though they're allowed to perform passage espionage on anyone. Similarly, the master cannot perform active espionage missions on his vassals.
  
• Master and vassal spies cannot be caught while passing through or idling in master's or the vassal's cultural boundaries.
  
• Vassal culture can occupy a master's city or a master's vassal's city, but it cannot force that city to flip. Any attempt to flip or revolt in this manner will simply prompt the master to see if they want to liberate the city to the proper civilization.
  
• Nobody can declare war on a vassal, and the vassal cannot declare war--all declarations and cries for peace go through the master.
  
• The master cannot go to war on his own vassals unless a vassal refuses to give up a resource, or the vassal has reached the necessary requirements for breaking the relationship. In other words, this remains as it is now.

For capitulated vassals only

• Capitulated vassals cannot trade technology, maps, resources, or gold with anyone except the master or the other capitulated vassals of that master. The capitulated vassal can refuse to trade technology and gold to the master, but that means it will have nobody to trade with except for any of the other capitulated vassals of the master. Similarly, the master can expect that after gifting technology and gold to his capitulated vassals, the technology and funds will remain secure.

For colonies and other peacetime vassals only

• Trade with anyone is allowed.

Commentary

Most of these behaviors are no different from the current system. It only looks like a lot of information because I've simply spelled them out. However, the "exploitative" elements of the vassal system are removed. It's easier to understand, and the AI for this would be less likely to fumble. The vassal balance would be more or less unchanged.

I think vassals are currently broken. I think this system fixes them. What do you think?

[OliverFA]

But why cannot a civilization capitulate to anyone they want? That is how many big conflicts have been created in history, by capitulating to bigger powers who were not involved in the war at first.

Other than that. I agree that the vassal system is the bigest (and probably the only one) disapointment in Civ4.

[Zoolooman]

Currently, the vassal system's worst feature is its AI. It has difficultly judging when to capitulate to the player versus capitulating to an AI war ally.

While playing Warlords and BTS for the last month, I've kept track of when and to whom the AI capitulated. Now, I commonly bring in war allies because it's fun. So far, with a new game played every five days and about ten recorded wars with war allies, the AI capitulated only twice to me and eight times to one of my war allies.

Why is this? In all cases, I've captured and razed more cities, and I generally represent the larger threat. But the AI suddenly surrenders to someone far away, and my soldiers have to stop their attack. This doesn't make sense.

In real life, I'd be able to call up my war ally and bargain with them for the new vassal, and in the worst case I could threaten to go to war on my ally if they take the vassal that I've rightfully defeated. But the vassal system is too simple to make this nuanced deliberation. It simply tosses peace at the player, and this is not fun. It discourages the player from bringing in war allies, because the AI will almost always capitulate to the war ally and abruptly end the war.

The best solution would introduce that moment of deliberation between the war allies. But because I don't trust the AI to make the decision properly, I think it's easier to simply assume that the warmonger who has fought the longest (or dealt the most harm) has earned the right of vassalage over the defeated foe.

[dsteve3]

(dare I tread on dangerous terrain? comparing Civ to Europa Universalis?)

In EU, vassals are only really useful in a few instances:

1) If the conquerred country is the same religion, and they are sufficiently smaller, there is a good chance I can diplomatically annex them in the future. This is a key to building certain empires.

2) If the conquered country is a different religion, then vassalization is only good to creating a buffer zone against big baddies that I don't want to boarder directly.

Of course, its alot easier to spread religion in Civ than in EU.

My enemy's vassals are a good bargaining chip in any diplomacy following a successful campaign - stripping enemies of vassals is a necessity. Forcing enemies to make vassals from non-accepted cultural provinces is also a great way to weaken them without outright conquest.

I don't have the new Civ expansion yet, so I'm not sure if this applies, but understanding vassals is a crucial aspect of EU. Can't really win the game without it.