I saw someone on another thread suggest vassal diplomacy as a relatively offhand comment but I thought it deserved a thread of its own.

Endless Legend presented minor factions and their diplomacy in a satisfactorily way but it was still generally regulated, except for one faction: the Cultists. While I'm not sure that the mechanics of vassals and minor factions would operate in the exact same way where a minor faction camp only effectively exists as a district extension which produces units; I am sure that creating the alternative of controlling the map through diplomatic relations with minor factions, assuming they will exist in any form(city-states or otherwise), in contrast to just individual city-expansion is an intriguing idea. That said however, vassals still could not be so strong as to delegitimize the necessity for player-to-player contact.

Notes on minor faction sophistication concepts and vassalage ideas:

Minor Faction [First Level] - Village/tribe:

Most minor factions begin game as inconsequential tribes/small villages and towns. At this level of influence these factions/independent cells are unable to lay claim to a territory and players can still claim their land. Player diplomacy is still very simplistic, maybe to the degree of endless legend minor faction diplomacy where they offer a single quest for pacification.

Minor Faction [Second Level] - City State:

Through the occurence of a specific event(s), the minor faction village morphs into a city-state capable of exploiting adjacent tiles, it can also produce and expand to a very simplistic degree constructing maybe a few districts outside. Missions can still be done as in the first level, but instead it provides diplomatic clout rather than direct pacification. The city-state's access to research is determined by the tech development of the median of the players in the game. At this level of sophistication, the city-state now possesses enough influence to prevent a player's claiming of the land. The city-state will also maintain a military and patrol the territories borders. The city-state will also tax and reduce the returns on players trade routes who pass through their borders. Players who decide to still enter the territory despite the minor faction's claim to it will be attacked by these patrols and relations will be hurt. The diplomatic capabilities of the city-state increase considerably: trade routes can be established but the returns will be less than a player (these are not taxed), a player could gift the city-state units to bolster their patrolling forces, resources can be traded although the city state can only trade the resources within its borders regardless of past trades with players and the city-state possesses a very limited supply of what they do have, city-states can also trade using a small reserve of resource packages for science, food, production, etc. however these are limited in number per player to avoid exploitation and slowly restock overtime. As players trade more with a city-state, the city-state also gains more favorable relations with the player and even eventually permits open borders. At a high enough level of relations, the city-state will be available for vassalization however this is a costly action which is partly discounted based on the military strength of the offering player in terms of the other players.

SOME NOTES:

City-states will be unable to offer up money and can only trade the resources within their borders or the aforementioned supply packages, this is in order to avoid player exploitation.

City-state trades do not become more favorable as relations increase but will become less favorable as diplomatic relations decrease.

City-states might make trade networks with the player of their own accord.

A city-state instead of capture can be forced into vassalage.

Ways for a minor faction to go from [Level 1] to [Level 2]:

-A random world event based upon the extensive existence or other factor, a tribe is also unable to ascend if a player has already constructed a city in the territory where it would have otherwise occurred.

-A player has such severe destabalization that the rebels who spawn in to attack a city manage to actually overpower the garrison. This results in the city becoming a city-state which possesses negative relations with the original owner. The city also has the same districts and expansions as before.

-A special event where due to over-expansion of a single player or tyrannical practices, a siege/uprising of tribal or independent persons rise up against the player who has built a city in a territory where a tribe/minor faction previously lived. If the siege of people occurs and they overtake the city, the city becomes a city-state similar to bullet 2.

Minor Faction [Third Level] - Vassal:

This city-state is the same as level 2 with a few minor changes.The city-state will provide tribute to the lord player. The city-state will not tax its player lord's trade routes. The city will also not trade with those who the player is actively at war with. Vassals cannot become vassals of other players. Vassals will also join in military conflicts against players that the lord player wages war against. That said, should a player fail to come to the aid of the vassals assistance if they are attacked, the city-state will immediately abolish the vassal relation and gain significantly negative relations with the player. The player is also able to abolish the vassal relation after a small delay which results in only a small degree of negative relations which uniquely recovers passively.

My own thoughts and plans on the matter are not as well developed as I would like and so suggest that if you have any interesting ideas, comments, or suggestions on how this could work that would make for interesting and smooth gameplay, post a comment. I personally feel that this idea is a fantastic concept that is worthy of discussion.