This guide will have every single minor faction currently in the game, as well as the variations that occur if you are playing as the Hissho, as they do not have Approval, they have Keii, which no minor faction gives, and they do not have the standard moods like Happy or Ecstatic, instead replacing those with Loyal and Devoted. In addition, due to not having approval ratings, Hissho do not suffer from overpopulation maluses like other factions, so things that affect that are changed as well.

There are 21 minor factions with the base game and free DLCs. The Harmony minor faction is included in the 'Lost Symphony' DLC, the Sisters of Mercy are included with the 'Vaulters' expansion, and the Illo are included in the 'Supremacy' expansion. Paid DLC factions will be indicated in the list.

In addition to the 24 total minor factions, you can assimilate population from the other major factions into your empire. Either through conquest or minor quests/events or finding them in curiosities. These populations do not have assimilation bonuses, but they do have their own political ideology as well as the standard 10/20/50 population bonuses. For the sake of organization, the major faction populations will be listed after the minor civilizations.

The format will be:

Ideology : Pacifists / Ecologists / Scientists / Industrialists / Militarists / Religious
- Excepting the Pilgrims, this ideology dictates what the 10 population collection boost will be.

Trait : Temperate / Pragmatists / Warmonger
- This trait affects what the fourth choice on their diplomacy screen will be.
- Temp = Selective Migration / Pragmatists = Dev Grants / War = Train Foreign Corps


Political Traits :

• +Ideology (except the Pilgrims, this will always be the same as their Ideology above)
  
• -Ideology (always a reduced feeling towards a particular ideology, except Amblyr and Pilgrims)
  
• X event == Y Ideology (except Yuusho)

Bonuses : (Hissho variations in parentheses)

• +2 Approval. (+20 Manpower)
  
• +2 Dust on Happy (Loyal)

Assimilation Bonus : (Hissho variations in parentheses)

• 50/70 : Empire wide boosts
  
• 20/70 : Empire wide boosts

- Note that a 50/70 chance is ~ 71%, it is the more common assimilation bonus.
20 / 50 population effects : (Hissho variations in parentheses)

• +x% thing
  
• Law or battle strategy (Major factions have empire wide bonuses)

- Note that the 20 pop bonus only affects systems with the requisite population on it. A population bonus of +15% Industry from having 20 Remnant will only affect systems that contain at least one population of Remnant. A system with 1 Remnant and another with 10 with both only gain +15% Industry. So diversifying populations is a good strategy.

- Laws are passed normally through the empire screen. They vary from somewhat useful to situationally useful, to rarely useful, to basically useless.
- Ground battle strategies are variations on existing strategies, usually slightly better.


-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Most of the Major Factions peacefully acquire Minor Factions in the same way. There are three ways to boost your relationship with them. The "Praise" function in their respective Diplomacy screen, where you directly spend Influence on them. Searching curiosities in their system gives you a small boost. Lastly is to have them under one (or more) of your systems influence area, you will slowly convert them. (Note: Custom factions can have the "Big Brother" trait, which increases your standing with Minor Factions as well).
Upon hitting 50 points in your relationship, you can do a small quest to assimilate them, some are easier to complete than others.
At 100 points, you can just straight up assimilate the faction and gain their bonus and their system.

If it is a faction you want to boost up, I recommend shipping them to your other systems whenever you can.

Some factions do things a bit differently.

Cravers

By default, Cravers cannot use Praise on Minor Factions. Their Endless War trait stops most diplomacy options. Though the in-game tooltip text states that you must have the Pacifist party leading your government in order to interact diplomatically, any party that gets votes from the pacifist party (Lesser represented political parties usually send their votes to one of the others), so even if you change to Industrialist, you can then interact with the minor factions.

So by default, the only way for Cravers to take a minor faction (as just exploring any curiosities doesn't give you enough points) is to declare war and invade. If you want to save the population, I recommend using the Guerrilla option to minimize pop losses.


Vodyani

Vodyani do not directly acquire minor factions the way other races are able to. The build up is still done the same way (3 ways to influence), and you can still acquire the assimilation trait, but instead of assimilating the system / population (and having access to that pop, you are given a different option: Brainwash. This is essentially the same as being their sovereign, they send you dust/science/manpower, but you do not acquire the system, and you do not have access to the civilian pops on your systems. In addition, they give you a small amount of essence per turn.
Factions that offer Foreign Corps or Development Grants still offer those, but Selective Migration is replaced with "Collect Essence Tribute" which sacrifices 1 unit of population for 100 essence (system must have 2+ pop to use).

Additionally, since you might want the system that a minor faction inhabits, Vodyani also get "Evacuate System" which removes the entire population of the system and generates military ship(s). Using this option completely removes that faction and its population from the game, so if you are using them to leech essence off of, the system under them should be better than however much essence they are providing.

Vodyani can also invade minor factions the same way as other factions, but cannot claim ownership of a system. They either pillage or their version of raze, "Hunting Grounds", which works the same way, but also provides Essence / turn for every turn that population or improvements still remain. (Note: there is also no Empire-wide Approval penalty on either Pillage or Raze for Vodyani)

Initial Publish - 2018-09-24
Update - 2018-09-30 - Added all missing Hissho specific information.
Update - 2018-10-06 - Added some notes about Vodyani specifics / partial splice guide.
Update - 2018-10-12 - Added the minor faction & Hissho splice information.
Update - 2019-02-24 - Added Penumbra DLC major faction / minor faction

Guide is complete (on major information) and up to date as of 1.3.14 S5 GOLD

To do : Add extra faction specific information where needed. Unfallen and finish Horatio splice chart. Need Umbral Choir and Kalmat splice info

All Minor Factions, including free and paid DLC.

Ideology : Pacifists

Trait : Temperate (Selective Migration)

Political Traits :

• +Pacifists
  
• Pacifist events == Industrialists
  
• Scientific events == Industrialists

Bonuses :

• +2 Industry on Sterile
  
• +1 Dust

Assimilation Bonus :

• 50/90 : +40 Dust per Strategic Resource on planet
  
• 40/90 : 10% Ship / Construction buyout reduction.

20 / 50 population effects :

• +10% Dust
  
• Law : +50% Deposit value on Luxury Resource Deposits

Ideology : Ecologists

Trait : Temperate (Selective Migration)
Political Traits :

• +Ecologists
  
• -Industrialists
  
• Industrialist events == Ecologists

Bonuses :

• +5 Food
  
• --

Assimilation Bonus :

• 50/70 : +10 Influence per Empires at Peace, +10 Influence per Empires in Alliance
  
• 20/70 : +0.1 Food per Industry on Systems

20 / 50 population effects :

• +15% Food
  
• Law : -50% Diplomatic Pressure

Ideology : Pacifists

Trait : Temperate (Selective Migration)
Political Traits :

• +Pacifists
  
• -Militarists
  
• Militarist events == Pacifists

Bonuses : (Hissho variations in parentheses)

• +1 Influence on Fertile
  
• --

Assimilation Bonus : (Hissho variations in parentheses)

• 50/70 : Systems are 25% more expensive to convert with Influence
  
• 20/70 : -10% Treaty cost per Empires at peace, -10% Treaty cost per Empires in Alliance

20 / 50 population effects : (Hissho variations in parentheses)

• +10% Influence
  
• Ground Battle Strategy - White Flag :No destruction on system, ownership change speed 25%

Ideology : Scientists

Trait : Pragmatists (Development Grants)
Political Traits :

• +Scientists
  
• -Religious
  
• Pacifist events == Scientists

Bonuses :

• +2 Science
  
• +5 Food on Gas

Assimilation Bonus :

• 50/70 : -10% Technology cost on Empire
  
• 20/70 : Set minimum Science on Systems to 5 if natural value is lower.

20 / 50 population effects :

• +15% Science
  
• Law : -30% Research cost on Empire Development Technology

Ideology : Ecologists

Trait : Warmonger (Train Foreign Corps)
Political Traits :

• +Ecologists
  
• -Industrialists
  
• Industrialist events == Ecologists

Bonuses :

• +1 Industry
  
• +5 Food on Sterile

Assimilation Bonus :

• 50/70 : -10% Peaceful Treaty cost
  
• 20/70 : +5% Trade Value on Systems

20 / 50 population effects :

• -20% Industry Cost
  
• Law : +20% Ownership recovery rate on systems

Ideology : Religious

Trait : Temperate (Selective Migration)
Political Traits :

• +Religious
  
• -Scientists
  
• Pacifist events == Religious

Bonuses :

• +1 Dust
  
• +5 Dust on Gas

Assimilation Bonus :

• 50/70 : +5 Dust per Curiosity discovered on Empire
  
• 20/70 : +25 Dust per Heroes on Empire

20 / 50 population effects :

• +15% Food
  
• Law : -50% Diplomatic Pressure

Ideology : Scientists

Trait : Temperate (Selective Migration)
Political Traits :

• +Scientists
  
• -Ecologists
  
• Industrial events == Scientists

Bonuses :

• +2 Science
  
• --

Assimilation Bonus :

• 50/70 : +40 Science per Strategic Deposit on Systems
  
• 20/70 : +20 Science on Cold on Systems +25% Deposit value on Strategic Resources

20 / 50 population effects : (Hissho variations in parentheses)

• +10% Science
  
• Law : 1% Technology cost reduction per Strategic Resource Deposit on Empire

Ideology : Militarists

Trait : Warmonger (Train Foreign Corps)
Political Traits :

• +Militarists
  
• -Pacifists
  
• Pacifist events == Militarist

Bonuses :

• +50 damage to Attackers on Ground
  
• +50 damage to Attackers on Ground on Fertile

Assimilation Bonus :

• 50/70 : +750 damage to Attackers on Ground
  
• 20/70 : +15% Infantry damage, +15% Infantry HP

20 / 50 population effects :

• +300 damage to Attackers on Ground
  
• Ground Battle Strategy : Militant Defense
  Defending Troops Max HP +30%
  Improvement Destruction Probability -25%
  Population Destruction Probability -25%
  Min Damage to Attacker +500
  Max Damage to Attacker +800

Notes
Starting Minor Faction of the Lumeris.

Ideology : Ecologists

Trait : Pragmatists (Development Grants)
Political Traits :

• +Ecologists
  
• -Religious
  
• Scientific events == Ecologists

Bonuses :

• +2 Science per Strategic Deposit
  
• +2 Food per Strategic Deposit

Assimilation Bonus :

• 50/70 : 10% of Food is converted to Science on Systems
  
• 20/70 : -20% Dust upkeep on Systems with Strategic Deposits

20 / 50 population effects : (Hissho variations in parentheses)

• +10% Science
  
• Law : +5 Approval per Strategic Deposits on Systems ( Hissho : +2% Bonus Keii gains after a space/ground battle per Strategic Deposits on Systems)

Ideology : Pacifists

Trait : Temperate (Selective Migration)
Political Traits :

• +Pacifists
  
• -Militarists
  
• Ecologist events == Pacifists

Bonuses :

• +1 Food
  
• +3 Food on Sterile

Assimilation Bonus :

• 50/70 : -10% Food Consumption on Systems
  
• 20/70 : Set minimum food on Systems to 5 if natural value is lower.

20 / 50 population effects :

• +10% Food
  
• Law : -20% Food used by existing populations.

Notes
Starting Minor Faction of the Cravers.

Ideology : Religious

Trait : Pragmatists (Development Grants)
Political Traits :

• +Religious
  
• -Industrialists
  
• Militarist events == Religious

Bonuses :

• +1 Influence on Hot
  
• --

Assimilation Bonus :

• 50/70 : +40 Influence per Behemoth on Empire
  
• 20/70 : -25% Dust Upkeep on Behemoth

20 / 50 population effects :

• +10% Influence
  
• Law : +5% Influence per War

Notes
Starting Minor Faction of the Hissho.

Ideology : Ecologists

Trait : Warmonger (Train Foreign Corps)
Political Traits :

• +Ecologists
  
• -Pacifists
  
• Religious events == Ecologists

Bonuses : (Hissho variations in parentheses)

• +4 Approval on Sterile (+20 Manpower Capacity on Sterile)
  
• +2 Approval (+20 Manpower Capacity)

Assimilation Bonus : (Hissho variations in parentheses)

• 50/70 : +10 Approval per Sterile on Systems, -25% Overpopulation disapproval
  (+5% Industry per Sterile on Systems)
  
• 20/70 : +1 Overcolonization Threshold

20 / 50 population effects : (Hissho variations in parentheses)

• +10 Approval (+50 Manpower per turn)
  
• Law : +0.25 Move speed on ships per Systems in Empire.

Ideology : Religious

Trait : Pragmatists (Development Grants)
Political Traits :

• +Religious
  
• -Scientists
  
• Pacifist events == Religious

Bonuses : (Hissho variations in parentheses)

• +2 Approval (+20 Manpower Capacity)
  
• +4 Approval on Fertile (+20 Manpower Capacity on Fertile)

Assimilation Bonus : (Hissho variations in parentheses)

• 50/70 : +20 Approval on Systems with Hero (Hissho : +20 Manpower per Hero on Systems)
  
• 20/70 : -20% System Level upgrade cost

20 / 50 population effects : (Hissho variations in parentheses)

• +20% Influence
  
• Law : No unhappiness from overpopulation. (Hissho : +20% Food to Manpower on Systems)

Ideology : Industrialist

Trait :
Political Traits :

• +Industrialists
  
• -Militarists
  
• Scientist events == Pacifist

Bonuses :

• +1 Bandwidth
  
• +1 Bandwidth on Small

Assimilation Bonus :

• 50/70 : -10% Bandwidth cost on Hacking Programs
  
• 20/70 : +10% Hacking Speed on Empire

20 / 50 population effects :

• +10% Industry
  
• Law : Societal Bandwidth: +20% Bandwidth on Empire.

Ideology : Industrialists

Trait : Pragmatists (Development Grants)
Political Traits :

• +Industrialists
  
• -Ecologists
  
• Militarist events == Industrialist

Bonuses :

• +1 Industry
  
• +2 Industry on Hot

Assimilation Bonus :

• 50/70 : -10% Ship Industry cost
  
• 20/70 : -10% System Improvement Industry cost

20 / 50 population effects : (Hissho variations in parentheses)

• +15% Industry
  
• Law : -50% Expansion Disapproval on Systems (Hissho : +2 Systems Occupied before triggering expansion disapproval)

Ideology : Ecologists

Trait : Temperate (Selective Migration)
Political Traits :

• +Ecologists
  
• -Industrialists
  
• Industrialist events == Ecologists

Bonuses :

• +2 Food
  
• +3 Food on Fertile

Assimilation Bonus : (Hissho variations in parentheses)

• 50/70 : +5 Approval per Fertile on Systems (Hissho - ???)
  
• 20/70 : +25% Food on Happy (Loyal), +25% Food on Ecstatic (Devoted)

20 / 50 population effects : (Hissho variations in parentheses)

• +15% Food
  
• Law : +5 Approval per System level, +1 Approval per population on Systems (Hissho : +3% Bonus Keii after Space/Ground battle per System Level on Systems)

Ideology : Religious

Trait : Temperate (Selective Migration)
Political Traits :

• +Scientists (**NOTE: This is different from their Ideology)
  
• +Religious (**NOTE: This is also a boost)
  
• Scientific events == Religious

Bonuses :

• +2 Science
  
• +3 Science on Anomaly

Assimilation Bonus :

• 50/70 : +50% Probe Speed and Vision
  
• 20/70 : +5 Science per Anomaly on Systems

10 / 20 / 50 population effects :

• +Scientists (This is different from their base ideology)
  
• +10 Vision Range
  
• Law : See All Fleets (Does not grant shared vision with fleets, only their location and makeup)

Notes
Starting Minor Faction of the Sophons.

Ideology : Industrialists

Trait : Temperate (Selective Migration)
Political Traits :

• +Industrialist
  
• -Ecologist
  
• Scientific events == Industrialist

Bonuses :

• +1 Industry
  
• +5 Science on Anomaly

Assimilation Bonus :

• 50/70 : +1 Industry per Curiosity Discovered on Empire
  
• 20/70 : -20% Science cost on facilitating link

20 / 50 population effects :

• +10% Industry
  
• Law : +0.1 Science per Industry on Systems

Ideology : Industrialists

Trait : Pragmatists (Development Grants)
Political Traits :

• +Industrialists
  
• -Ecologists
  
• Militarist events == Industrialist

Bonuses :

• +1 Industry
  
• +2 Dust on Happy (Loyal)

Assimilation Bonus :

• 50/70 : -10% Wonder Industry cost
  
• 20/70 : -35% Improvement Destruction on Systems

20 / 50 population effects :

• +15% Industry
  
• Law : +50% Deposit value on Strategic Deposits

Notes
Starting Minor Faction of the Riftborn.

Ideology : Industrialists

Trait : Temperate (Selective Migration)
Political Traits :

• +Industrialist
  
• -Militarist
  
• Ecologist events == Industrialist

Bonuses :

• +2 Industry on Fertile
  
• +1 Industry

Assimilation Bonus :

• 50/85 : +25 Industry per Anomaly on Systems
  
• 35/85 : +20 Science per System Level on Systems, +50% Luxury Deposit value on Fertile

20 / 50 population effects :

• +10% Industry
  
• Law : -10% System Improvement Industry cost per Luxury Deposit on Systems

Ideology : Religious

Trait : Pragmatists (Development Grants)
Political Traits :

• +Religious
  
• -Industrialists
  
• Militarist events == Religious

Bonuses : (Hissho variations in parentheses)

• +20 damage to Attackers on Ground
  
• +2 Approval (+20 Manpower Capacity)

Assimilation Bonus :

• 50/70 : +50% Recovery Speed on Heroes
  
• 20/70 : +10 Regeneration on Ships

20 / 50 population effects : (Hissho variations in parentheses)

• +20% HP Regeneration on Ships
  
• Law : +25% HP of Defending Troops in Ground Battle

Notes
Starting Minor Faction of the Vaulters.

Ideology : Religious

Trait : Pragmatists (Development Grants)
Political Traits :

• +Religious
  
• -Scientists
  
• Industrialist events == Ecologists

Bonuses :

• +2 Food
  
• -1 Depletion Points per Turn

Assimilation Bonus :

• 50/85 : +25 Food per Sterile, +2 FIDSI per Population on Planets with Reduced Anomalies
  
• 35/85 : -50% Terraforming cost

20 / 50 population effects :

• +10% Food
  
• Law : +5% FIDS per Fertile planet on Systems

Notes
As with all populations, using a booster doubles their effect (so +4 food / -2 Depletion points). If you have the luxury resources to allow it, you can have 1 Sower pop to 2 Craver pop, or if they are 1:1, then you gain back depletion points.

Whatever you do, if you are playing as Cravers, you should definitely try to assimilate them and shuffle them around to systems. Be careful of Slave driving unhappiness though.

Ideology : Militarists

Trait : Warmongers (Train Foreign Corps)
Political Traits :

• +Militarists
  
• -Pacifists
  
• Industrialist events == Militarist

Bonuses :

• +5 Manpower replenishment per turn
  
• +5 Manpower replenishment per turn on Fertile

Assimilation Bonus :

• 50/70 : 17.5% More Infantry on Ground Battle
  
• 20/70 : 100 Manpower replenishment per turn

20 / 50 population effects :

• +50 Manpower
  
• Ground Battle Strategy - Swarm Assault
  Attacker Troops Max HP -20%
  Improve Destroy Probability +25%
  Pop Destroy Probability +25%
  Bombardment Dmg to Def 10%
  Manpower Deploy Limit 40%

Ideology : Militarists

Trait : Warmongers (Train Foreign Corps)
Political Traits :

• +Militarists
  
• -Pacifists
  
• -Scientists

Bonuses :

• +20 Manpower
  
• +30 Manpower on Sterile

Assimilation Bonus :

• 50/70 : +20% damage on Weapon modules
  
• 20/70 : -10% Manpower cost per troops on ground battle

20 / 50 population effects :

• +15% Manpower Capacity
  
• Law: 15% Manpower Replenishment on Fleets outside borders

Notes
Starting Minor Faction of the United Empire.

Ideology : Scientists

Trait : Pragmatists (Development Grants)
Political Traits :

• +Scientists
  
• -Religious
  
• Industrialist events == Scientists

Bonuses : (Hissho variations in parentheses)

• +2 Approval (+1 Science)
  
• +3 Science on Happy (Loyal)

Assimilation Bonus : (Hissho variations in parentheses)

• 50/70 : +5 Approval (+5% Industry) per stage unlocked in Science & Exploration
  
• 20/70 : -25% Diplomatic Pressure

20 / 50 population effects : (Hissho variations in parentheses)

• +10% Science on Happy (Loyal), +20% Science on Ecstatic (Devoted)
  
• Law : 0% Blockade Impact Factor

Notes
Starting Minor Faction of the Horatio.

Ideology : Militarists

Political Traits :

• +Militarists
  
• -Pacifists
  
• Pacifist events == Militarist

Bonuses :

• +150% FIDS on undepleted planet
  
• +1 Depletion point per turn

20 / 50 population effects :

• -10% Ship Industry cost
  
• +1% Damage per Depleted planet on Empire

Notes
Even if you aren't playing as the Cravers, if you have Craver pop on planets, they will deplete it.

The absolute easiest way to remove annoying Craver pops so they don't deplete your planets is to load them up on a ship to a full system, and then destroy the migration ship with your privateers. (T4 Military tech - Deniable Operations // Vaulters get them by default). Alternatively, if you ship them off to an out of the way full system, you can also just ignore the migration ship and let it sit outside of the system forever.

If you are the Hissho (or a faction that refuses pirate diplomacy), then you must evacuate the system after ownership changes.

If you have access to Sower minor faction pop, you could attempt to send them both off to a system together and keep them 1:1, but micro-managing the population might be a bit time consuming or tricky.

Ideology : Ecologists

Political Traits :

• +Ecologists
  
• -Scientists
  

Bonuses :

• +3 Food
  
• +2 Approval on Hot (+1 Influence on Hot)

20 / 50 population effects :

• +15% Food
  
• 5% Food to Influence on Systems

Notes

Splicing gives a reduced bonus similar to what the minor/major faction provides.

Major Factions (Partially Incomplete)

• Cravers : +5% FIDS
  
• Horatio : +2 Food, +1 Happiness
  
• Hissho : +2 Industry, +1 Manpower
  
• Lumeris : +2 Dust
  
• Riftborn : +2 Industry, +2 Dust, +2 Science
  
• Sophons: +2 Science
  
• Unfallen : +2 Food
  
• -- Guardians : N/A (Cannot be spliced)
  
• Umbral Choir :
  
• UE - Imperials : +1 Influence
  
• UE - Sheredyn : +15 Manpower
  
• UE - Mezari : +2 Science
  
• Vaulters : +1 Science, +10 Damage in ground battle
  
• -- Bereaved : ??
  
• -- Foundlings : ??
  
• Vodyani : +2 FIDS

Minor Factions

• Amblyr : +1 Industry, +1 Dust
  
• Amoeba : +3 Food
  
• Bhagaba : +1 Influence
  
• Deuyivans : +1 Food, +2 Science
  
• Epistis : +1 Food, +2 Industry
  
• Eyder : +2 Dust
  
• Galvran : +2 Science
  
• Gnashast : +50 Damage in ground battle
  
• Harmony : +2 Science, +2 Food
  
• Haroshem : +3 Food
  
• Illo : +1 Influence
  
• Kal'Tik'Ma : +3 Approval
  
• Kalgeros : +3 Happiness
  
• Kalmat :
  
• Mavros : +3 Industry
  
• Niris : +2 Food
  
• Pilgrims : +3 Science
  
• Pulsos : +2 Industry, +1 Science
  
• Remnants : +2 Industry, +1 Dust
  
• Sefaloros : +3 Industry
  
• Sisters of Mercy : +10 Damage done to Attacker during Ground Battle, +2 Approval
  
• Sowers : -1 Depletion points per turn on Planets, +1 Food
  
• Tikanan : +5 Manpower per turn
  
• Yuusho : +15 Manpower
  
• Z'vali : +1 Science +2 Approval

Notes
The Faction quest line for the Imperials will give you a choice of either staying as the Imperials or changing the entire population to Mezari or Sheredyn. I don't know what happens if you have Imperial pop on your Empire and an Empire player changes their pop to Mezari or Sheredyn if it affects yours. I've read that you can (but not personally tried) to save some standard Imperial pop if they are in transit between systems when you make the choice between the three pops.


Ideology : Industrialists

Political Traits :

• +Industrialists
  
• -Ecologists
  
• Scientist events == Industrialist

Bonuses :

• +1 Influence
  
• --

20 / 50 population effects :

• +15% Influence
  
• +0.1 Influence per Industry Spent

Ideology : Scientists

Political Traits :

• +Scientists
  
• -Religious
  
• Pacifist events == Scientists

Bonuses :

• +1 Science
  
• +0.5 Influence

20 / 50 population effects :

• +10% Science
  
• -10% Technology cost

Ideology : Militarists

Political Traits :

• +Militarists
  
• -Pacifists
  
• Pacifist events == Militarist

Bonuses :

• +20 Manpower
  
• +0.5 Influence

20 / 50 population effects :

• +15% Manpower Capacity
  
• +5 Influence per 100 Manpower on System

Ideology : Pacifists

Political Traits :

• +Pacifists
  
• -Militarists
  
• Ecologist events == Pacifist

Bonuses :

• +3 Dust on Fertile
  
• +1 Dust

20 / 50 population effects :

• -15% Dust
  
• Ignore Blockades on trade routes

Notes Riftborn pop must be built, so if you happen to get one as a non-Riftborn faction, you probably won't get more.

Ideology : Industrialists

Political Traits :

• +Industrialists
  
• -Ecologists
  
• Scientist events == Industrialist

Bonuses :

• +5 Industry / Dust / Science
  

20 / 50 population effects :

• +15% Industry
  
• Wormhole travel only consumes half of remaining movement points.

Ideology : Scientists

Political Traits :

• +Scientists
  
• -Religious
  
• Pacifist events == Scientists

Bonuses :

• +3 Science on Cold
  
• +1 Science

20 / 50 population effects :

• +15% Science
  
• -20% Technology costs

Ideology : Pacifists

Political Traits :

• +Pacifists
  
• -Militarists
  
• Pacifist events == Science

Bonuses :

• +1 Science
  
• +4 Bandwidth

20 / 50 population effects : (Hissho variations in parentheses)

• +1 Influence per Allocated Bandwidth Points; +15 Bandwidth (Hissho: ?)
  
• +15% Hacking Speed on Empire

Ideology : Pacifists

Political Traits :

• +Pacifists
  
• -Industrialists
  
• Ecologist events == Pacifist

Bonuses :

• +2 Food
  
• +5 Food on Fertile

20 / 50 population effects :

• +15% Influence
  
• +50% Ownership recovery rate

Notes
To my understanding, Guardians only spawn in galaxies with the Unfallen as a faction (or a custom Faction with their trait). They only spawn on Boreal, Jungle, Toxic, Monsoon, Forest, Terran, and can only be discovered via curiosity by the faction with the "Guardians" trait. (Though you can get lucky with a "explore all curiosities" Curiosity) They are somewhat rare, which is why their pop bonuses are at 5/10/20, rather than the 10/20/50 of every other faction.

From the outside, there is no way to tell if a system that has been explored by the Unfallen has a Guardian. There will definitely be one on their home system, but otherwise until you conquer the planet, you will not know if a Guardian is there or not.

Ideology : Pacifists

Political Traits :

• +Pacifists
  
• -Militarist
  
• Ecologist events == Pacifist

Bonuses : (Hissho variation in parentheses)

• +200 damage on Ground Battle
  
• +5 Approval (Hissho : +10 Food)

10 / 20 population effects : (Note that Guardian bonuses are at 5/10/20 pop)

• +10 Approval (Hissho : +10% Food)
  
• -50% Peaceful Treaty Cost

Ideology : Religious

Political Traits :

• +Religious
  
• -Scientists
  
• Militarist events == Religious

Bonuses :

• +4 FIDS (Food / Industry / Dust / Science)
  
• -50% Food on System

20 / 50 population effects :

• +5% FIDSI (Food / Industry / Dust / Science / Influence)
  
• 100% Hero Recovery Rate

Notes:

Due to their massive Food penalty on the whole system, you might want them gone if you happen to get a refugee or if you conquer a system of theirs. Like above for Craver pop, the easiest way to get rid of them is to ship them to a full system and blow up the ship with privateers. (Or send them through pirate space). Alternatively, if you don't have access to privateers or full systems to let them rot around, ship them to your furthest away system, the civilian ship will take a while depending on the size of the galaxy you are playing as.

Notes
On the quest for Auriga / Auriga 2.0, part of the faction quest for the Vaulters, you will either get the Bereaved or the Foundlings as a separate population. Unlike the Imperials, your primary population doesn't change.


Ideology : Scientists

Political Traits :

• +Scientists
  
• -Ecologists
  
• Militarist events == Scientists

Bonuses :

• +25 damage to Attacker on Ground Battle
  
• +1 Science

20 / 50 population effects :

• +10% Science
  
• +0.1 Science per Manpower on Systems

Ideology : Militarists

Political Traits :

• +Militarists
  
• -Pacifists
  
• Scientist events == Militarist

Bonuses :

• +3 Science on Cold
  
• +20 Manpower

20 / 50 population effects :

• +15% Manpower
  
• +15% Manpower capacity on Empire

Ideology : Scientists

Political Traits :

• +Scientists
  
• -Religious
  
• Militarist events == Scientists

Bonuses :

• +3 Science
  
• --

20 / 50 population effects :

• +10% Science
  
• +2 Movement on Ships

Ideology : Militarists

Political Traits :

• +Militarist
  
• -Pacifist
  
• Religious events == Militarist

Bonuses :

• +2 Manpower per Turn
  
• +1 Industry per Turn

20 / 50 population effects :

• +15% Manpower per turn
  
• -25% Ship cost on Empire

In a big enough galaxy, or if the "unique" flag is turned off for minor factions generation, you can find multiple copies of the minor factions, and their assimilation bonuses do stack if you can get them both.

There are definitely some really good Assimilation bonuses, like the Yuusho +20% damage on weapon modules, if you plan on fighting a lot. Mavros have construction bonuses.

Assimilating Haroshem if they have their common -10% Food Consumption bonus can work really well if you want to expand wide, and in a big galaxy, you might be able to find two of them. You especially want to find them if you are playing as Vaulters with their Food penalty.

The Harmony's common Assimilation bonus (10% Food turned into Science) is generally awful in the early game when you want as much food as possible to expand. Unless you are Riftborn and you aren't terribly concerned with your minor pops anyway.

The Niris uncommon Assimilation bonus can definitely help boost population and help with expansion if you can keep the systems happy.

The Pulsos common Assimilation bonus can be exploited for significant boosts to early system growth. +1 Industry per curiosity discovered on empire means if you send a fleet of explorers out to spam curiosities, you can boost your industry significantly on newly colonized systems.

As mentioned in the intro, Minor Faction laws vary from Somewhat useful to situationally useful, to basically useless.

A notable exception is the Niris law, "Zero Tolerance Waste Act" which gives +5 Approval per System Level (so potentially a flat +5/10/15/20 approval bonus), as well as +1 Approval per pop on Systems, which can help counter some of the less desirable planets Approval penalties such as if you want to save a system of mostly Lava/Ash planets as an industry heavy ship factory.

A second notable exception is the Sowers law, which in a long game, might be worth boosting their pop growth for the benefits it gives. Sow & Reap - Output Maximization Program, +5% FIDS per Fertile planet on systems. 5% isn't much by itself, but the law is per fertile planet on systems, meaning that 2 fertile planets in a system gives a 10% FIDS boost, 3 gives 15%, up to a maximum of 25% on a system with 5 fertile planets.
Note though that this law is useless for the Riftborn, as they terraform away from Fertile planets.

I put together a spreadsheet to compile all of this information from various sources and from my own playing the game.

docs.google.com/spreadsheets/d/1ySkI4sGORsW3764UNWXIEVFwhmp1TW1kcj0E68aNPCE/edit?usp=sharing