Thank you. I note you've got over 2k soldiers at Fort Sera; I thought I'd reached a point around 200 where they stopped adding power. I'll have to try again.
Some donated captives still add +1 power to Fort Sera. These are the ID 5-15 captives. Try donating a Hulk, or Injured Hulk, or a Black Gunner.
Here is an old list of those enemies (from nouseforaname3, with final additions by me):
1. "Order of the Red Tide" (Marston Fort): Everyone but the young swordsman and the Shildaro, have an id which is at least 5;
2. "Hide your Daughters" (Marston Fort): Warlord (7);
3. "Lonely Rangers" (Marston Fort): Space Marine (7) and Sharpshooter (5) at the first position (other Sharpshooter are "worthless");
4. Last marston fort Bandit group: Raider Chief (5);
5. Neo Mexican Cartel (Stokke Fort): El Capataz (7), "Knife" Soldado (7), Brawler (7);
6. "Riffraff" (Stokke Fort): Veteran Thug (7), Thug (7), Brawler (7);
7. "Celior Looters" (Stokke Fort): Celior King (10) and Raider Chief (5);
8. Last stokke fort Bandit Group: Raider King (7) and Raider Chief (5);
9. Darkmere Highwayman (respawnable with 5 enemies): Highway Captain (7) and Highwayman at position 4 and 5 (5 each), the two others are only a 4;
10. Stokke Hills respawnable bandits (lower left corner): Raider Chief (5), but to meet him, one must engage the group between 7 pm and before midnight;
11. Scavenging ambush: Cocky Youth (5), all others are lower
12. Swamptribe: Only the Sampking and the not spawnable Swamp Prince have a high enough id (the Swamp Prince does not spawn, as the number of remaining swamptribe members is never a multiple of 4).
From the Bandit Subfactions (Kasey Park Robbers, Dockyard Punks and Redhaven Tigers) only the Punk King (5; Kasey Park Robbers) and the Alpha Tiger (7; Redhaven Tigers) have a high enough id. From Almers Karate School only the Karate Master is not a "wuss" and has an id of 5. [...] From the Black Scorpion groups, only the enemy at positions 1 is always an eight (all others are 0); from the Wrangler group, you would want the Wrangler; and you might also want Damian Watts from the group with Zenobia, as he also has an id high enough to boost the power of Fort Sera by 1 (if power is already 100).
Additional ones: The named guy in tier 6 and 7 bounties. Then the HULK, Injured HULK, Ultra HULK, Black Gunner, and Cyber Lord from Tier 6 and 7 bounties.
how do you know exactly what factions are worth and when and how to invest on them?
There's only four factions that do this scaling income. Fort Sera, Warrior's Hall (Aesir), The Great Mosque (Muslim) although you cannot own the faction and stops at 70 Standing, and The Holy Virgin (Catholic). Warrior's Hall accepts slaves and swords, the Mosque is the slowest since you mostly donate merchandise, and the Catholic Church accepts rations. And Fort Sera has worse power value to income conversion, in exchange for converting 100% of its power value to your household power value. (What does your house's power value do? Nothing much except for some story events check, e.g. getting Tori, but the household power value to clear those is not that high. At 10,000 household power value, you gain the Masters of Raana achievement. It does nothing, but it's an achievement.)
Warrior's Hall is the fastest to pump but it is also an opportunity cost problem. Every production points and steel you spend crafting swords is production points not creating a weapon to sell. If your best-selling weapons have reached 15,000 market supply, have at it while you wait for the market supply to slowly lower again, or if you just want to have passive income and not have to think about it. You need to be Aesir to donate, which is not a problem since Aesir has combat bonuses at high devotion.
The Catholic Church is slow but, after Zapin Fields is fully set up, its literally just the rations that your house accumulates after so many days. They also consider Aesir an enemy religion, so you cannot donate.
The Mosque accepts most religions, I think, but hoarding merchandise is even slower.
