I posted this up in the 2K games forums some time ago, but really want it to get attention, as this is very important to me (Link on 2K games forums: https://forums.2k.com/showthread.php?4281037-Please-consider-Vassalage)... Civilizations IV had a cool feature that I still sorely miss, where you could literally make another civ your vassal...Instead of writing out the entire thing myself, I found, copied and pasted something on the subject from the Civfanatics Forums. Credit for this write up goes to the Civfanatics member Crighton. Here is the link, which I encourage you all to read because it covers a lot more information than what I cut from it: http://www.civfanatics.com/civ4/strategy/vassals.php *** The Warlords expansion (Civilization IV) introduces a new diplomatic option called Vassal State. Vassal states are like an "asymmetric alliance" between two Civs. Basically, one civilization serves as the master in the relationship and collects tribute from the weaker, vassal nation. After the discovery of Feudalism the Vassal State option becomes available in the Diplomacy menu. There are two ways to acquire a vassal state, voluntary Vassal-ing, and Non-voluntary (Capitulated) Vassal-ing. The second acquisition method is more common, basically consisting of skull-thumping another Civ until it cries “uncle” and begs for mercy. At which point the losing Civ Capitulates to the winning Civ sacrificing it’s independence for mere survival and a chance (usually small) at one day regaining independence. A Vassal State that has Capitulated does not get the option to voluntarily end the Vassal agreement unless certain conditions are met. The less common method occurs during peacetime where a relatively small and weak Civ tries to partner up with a much more powerful Civ, and in exchange for protection agrees to become a Vassal State. A Civ which becomes a Vassal State during peace time is given the opportunity every 10 turns to end the agreement. Throughout long and turbulent games some states may routinely enter into and out of being a Vassal State frequently. When a Voluntary Vassal decides to secede the Master Civ is given the option of simply allowing the Vassal State to become independent, or can choose to protest this decision, in which case both states then become locked in a state of war. In both cases, a Vassal State may choose to break the Vassal agreement when any of the three following conditions occur: Condition 1: The Vassal State looses more than half of it’s territory that it owned at the time it became a Vassal State. For example: Monty become your Vassal and has 4 cities when he becomes your Vassal. Over time Monty grows his Civ to 8 cities total. If Monty looses 4 of his cities through war or culture flipping, he still has 4 cities left and cannot break the agreement. If he lost 6 of his 8 cities he will then have lost 50% of his original lands and can then choose to end the agreement (usually with some terse statement about “not being able to protect us.”) It should also be noted that if your Vassal looses cities, etc. to YOU through culture flipping THAT also counts towards the loss of territory condition. Condition 2: The Vassal State grows in size AND population to a point where it has more than 50% of the Master Civ’s size AND population. It’s important to reiterate that this is a two part condition. BOTH have to be met in order for this option to become available to the Vassal. Condition 3: This is a minor possibility which can occur, where the Master demands a particular resource and the Vassal refuses the Masters request, in which case the two states are at war. This does happen, but it hasn’t happened to me since I try to eliminate any potential escape route for my new pets. Since the Master can demand any single resource from the Vassal and the Vassal can’t refuse this single / first demand it’s best to choose the resource carefully, i.e. a strategic resource of some sort. Let’s say you’re in the classical or medieval era and need your Vassal’s horse resource so you demand and take. But later on you somehow lose your source of iron and demand it from your Vassal, he can refuse and break the Vassal agreement. So plan ahead when it comes to your resource requests. And by the way there is nothing to stop you from selling the horse back to your Vassal. Should a Vassal choose to break the agreement due to the above conditions listed above, the Vassals Master may not agree to peaceably allow the Vassal to become independent, in which case a state of war exists between the two Civs. Regrettably, there is currently no method to Release a Vassal from your control, so weigh your decision carefully before accepting a Vassal. [This statement is true as of and up to the v2.08 patch, you’d think this would be an obvious feature to include in the game considering it would make things more logically consistent AND reflect actual history, but whatever]. Theoretically it is possible to actually aggravate your vassal into refusing a resource demand at which point the Master could then decide to let the Vassal go or go to war with the now ex-Vassal IF the Vassal refuses the resource demand. Some basic pro’s of acquiring a Vassal: *The master enjoys complete freedom of movement in the vassal's territory, including the ability to heal normally in the vassal's territory and use fortifications owned by the vassal. The master can also investigate any vassal city. And as of the v2.08 patch the Master can now Airlift units directly into a Vassal’s cities. The Master no longer has to pay supply costs for units inside of the Vassal’s lands. However, the Master must agree to an Open Borders agreement with the Vassal in order for the Vassal to move units into and out of the Master’s territory. *The master can demand any SINGLE resource from a vassal, even one that the vassal is using. The vassal has the right to refuse the SECOND demand but if they do the two states are immediately at war. This can come in handy if your Vassal has the only strategic resource available to you: i.e. Copper, Iron, Horses, Oil, Aluminum, etc. Just remember to plan ahead if the resource will lose it’s strategic value (cough horses cough). *The master's people enjoy increased happiness. Those in the vassal empire suffer decreased happiness (but frankly who cares about that bit, it only acts as an incentive for the Vassal to purchase luxury goods from the Master to placate the populace and so long as you keep your Vassal under heel then it’s his problem). *The vassal can't make war or peace on its own. It immediately adopts the master's war and peace relationships. *Half of the vassal's territory and population count towards the master's domination victory AND score. Which can truly speed up a Domination or Conquest win. *You can rehabilitate your relationship over time with the Vassal Civ through normal diplomatic means, i.e. Open borders, Shared State Religions, Mutual Military Struggle (if battling another Civ), occasional gifts, etc. Also, after the v2.08 patch the Mutual Defense Pact bonus is now added into the diplomatic modifier between you and your vassal. The Downside of having a Vassal(s): *Having vassal cities will incur higher maintenance cost for your own cities. And if someone could find me the actual formula so I can provide a clear example of this I (and anyone else who reads this) would greatly appreciate it. Regardless of what the formula is put some extra thought into your economy to counter any uptick in maintenance costs. *Other civs may like you a little less when you have a vassal. You will most likely see a -1 Diplomacy Penalty in you relations with other Civ’s as they “Fear their Rivals becoming your Vassal.” This penalty is somewhat relative to the power of the Vassal-ed Civ. But regardless, if you have 3 Vassal’s of even modest power expect a -3 penalty with every other Civ left. *Similarly, a Vassal who has gone around the continent stirring up trouble is not going to be a good choice to become a Voluntary Vassal as the other Civ’s will view your patronage as if you were allies. The AI hatred of your Vassal may override their friendly feelings towards you. *Although you can direct what your Vassal researches the Vassal’s Master doesn’t share in the discovery. So if your vassal somehow manages to acquire some technology you don’t have, he doesn’t have to share it with you, nor can you compel the Vassal into sharing the tech. This is the complete opposite of the same occurrence during a Permanent Alliance, where the two allies can research different techs and the discoveries are shared between the two. *** This really needs to be discussed, and it is the number one feature I wish most to see added to Civilization VI. There should be a few slight changes as well, such as being able to release a vassal without provoking them into demanding their freedom, which is a good reason why we should talk about this in a focused discussion so we can both fit it for Civilization VI as well as maybe making it even better than how it is in IV. - Please note that "Vassalage" is absolutely nothing like the "Puppet City" option already in Civilization V. Potential idea for discussion: Your vassal provides you with uniques from their civ, such as unique units and unique buildings (real life example: England received longbowmen from their vassal Wales). Gedemon suggested the following awesome idea: Hegemony Victory, where you win by dominating via use of the Vassalage function. Please feel free to discuss this as well!