Lately a big topic has been faction differentiation. So I thought I would gather up some my ideas from other posts and update them. I think that instead of tons of little custom things like items which are really only visual in nature the actual play style of factions could be made more unique more efficiently by giving factions better and more powerful traits that allow them to implement unique strategies. The existing traits either unlock a single starting tech, which only effects the very beginning of the game, or are small multipliers. The key to unique factions is allowing them different play styles and options not giving them slightly different items or miniscule multipliers. Not only should each faction play differently but they should also each be different when you interact with them in game.
Altar: Is the champion faction so they need traits that encourage heavy use of champions.
-Fellowship: Reduces the experience penalty for multiple champions in an army.
-Celebrity: Champions above lv5 grant +0.5 faction prestige.
Capitar: Is the trading team so they should have traits that allow them to play a trade and gold based strategy.
-Finance: Gives interest on total gold.
-Factoring: Grants a Factor House improvement that creates a trade route to the main city. Or could boost gold from Economic treaties.
Gilden: They are the mining and production team. All about building up industry and developing the land.
-Industry: All Mines and Foundries also boost growth of the nearest city by +0.2.
-Craftsmen: Cost of upgrading units and purchasing equipment halved.
Pariden: The arrogant research team. They are also good at expanding because they believe the world should belong to them.
-Manifest Destiny: Other factions can't settle within 5 tiles of your territory.
-Decal: Grants Lorehold, a cheap improvement that gives +3 research, one per city.
Tarth: They are isolationists who use the land to their advantage.
-Reclusive: Other factions can't see or use roads in your territory. Or maybe they don't get roads, but get a movement bonus in their territory and ignore terrain penalties instead .
-Hunters: Food bonus from woods when placing cities. Or unlocks a improvement that boosts food but can only be built on forest.
Kraxis:The defensive/creeping team. They slowly expand their territory by placing outposts.
-Defensive: City levels grant bonuses to defenders as before. Forts and Castles boost food.
-Territorial: Provides a militia unit to all armies in friendly territory, and outposts territory radius expanded by 1.
Magnar: The Raiding and slaver team. Not built for expanding but still aggressive.
-Slavelords: Same, already the most unique faction trait. Grants population in capital from razing cities, and reduces food costs. You could maybe also add pop bonuses from destroying improvements, conquering cities, and winning battles.
-Raiders: Gain their territory bonus when in other players' territory.
Roseln: The magic and religious team. A tall civilization. Not aggressive but still a late game threat.
-Death Magic: Same, grants several death spells.
-Theocracy: The level of a city reduces its unrest.
Umber: The beast and horde team. The most populace fallen race so they are good at city spam.
- Serpents Pact: Same allows you to recruit lizard monsters.
-Migration: +0.3 growth in all cities.
Yithril: The powerful warrior faction. All about building up an elite army of unstoppable giants.
-Powerful: Same, grants Strength.
- Pillage: Grants resources and research for defeating other players and taking cities.
These are my ideas for some interesting and unique faction traits that would make each faction play differently. Feel free to brainstorm and post your ideas as well. Not only traits but what you believe the strategy or characteristics of each faction should be.