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Rules and Algorithm (Principia Moderni IV Map Game)

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The Rules of PMIV. It is mandatory to follow them at all times while moderating or playing the game. Here also lies the algorithm of PMIV, the method in which conflicts and battles are resolved. It's important to learn the algorithm, or algo for short, to learn the vitals of the game itself.


  1. It's strongly recommended to read up on your nation or region during the time period, and if you join later on in the game, learn the history of your region from archived turns.
  2. If a moderator be inactive in his duties for at least ten years in game, he will be considered as “honorary moderator” and will not have power unless requesting a return to the game with serious commitment.
  3. You only have two turns in-game to protest an implausible action. After this, the events taken place are deemed canon. However, if plausibility has suffered a big enough injury, a total of a ten turn retcon can take place with a moderator super majority.
  4. A player can be completely removed from the nation if they are inactive for five days. If their post is more than 70% identical (copy pasted) for a week and unresponsive, they can be considered for removal from the game.
  5. If two nations are in a personal union and are culturally similar, then after fifty years in personal union, the leading nation may choose to merge the two nations.
  6. You have one "free" switch to another nation every 100 years. You can also switch if your nation has been forcefully vassalized / conquered.

Time-specific Rules

  1. Until 1600, a nation may only have three historically accurate allies which must be listed here. Coalitions against an aggressive, growing nations may contain up to six nations. Coalitions must be historically accurate and can be moderated.
  2. If any mod discovers a colonial claims map before the New World is discovered, the players involved will be banned indefinitely.

Moderator Rules

  1. Burden of proof of plausibility is put on the player, not the moderator.
  2. Moderators cannot use absolutely any moderator powers in the region that they are playing in.
  3. Any change on the rules must be approved by a majority of the moderators.
  4. If an annual event or moderator response is a question, the moderators must hold a council. The council will decide the outcome with a super majority vote.
  5. In the end, moderator decision is final.


There will be one algorithm, for every front, every year turn a war carries on. This carries on until a treaty is signed or total victory is achieved by the victors. There are two stages to every algorithm—the pre-war stage, and the battle stage. The battle stage may be repeated up to six times per year, depending on how large the war is, in population and nation size.

As a side note — a nation may either call in an ally as a co-belligerent or as a regular ally. If a nation calls an ally in as a co-belligerent, the co-belligerent may call in other allies. If called in as a regular ally, the regular ally may not call in their allies. This system has some implications later on — see below.

Also note that a major war is classified as such when the population of the smaller side is 45% or more of the larger side. Any other war is considered a minor war.

Pre-War Stage


The first thing done is an algo is that the population is found of the entire alliance for both sides—leading nation, allies and vassals. 

  • 0.02+ every 10,000 people

War Exhaustion

War exhaustion is based on how many years at war a nation has been at. Every year a nation is at major war, war exhaustion increases by six. Every year a nation is at minor war, war exhaustion increases by one. Every year a nation is at peace, war exhaustion decreases by one, until it stops at zero.

  • -1 time the War Exhaustion score of Leading Nation.

Casus Belli

The motive for war, or Casus Belli. For this section, the most applicable motive must be chosen, not necessarily the one with the highest score. This section is only for leading nations, not allies.

  • Patriotic rebellion: +7
  • Religious War (Theocracies): +5
  • Reconquering historical holdings: +4
  • War for a Crown: +3
  • Attacking historic enemy: +3
  • Seizing a colony: +2
  • Trade war: +2
  • Conquering holdings that have no connection to attacker: +1

There are two parts to this. First, whether the attack on the defenders is an existential threat or not, and the regular motive section. Pick a casus belli from Part One and another casus belli from Part Two.

  • Part One
    • Existential threat (Country's existence is at threat): +2
    • Non-existential threat: 0
  • Part Two
    • Defending historical lands: +5
    • Defending the Crown: +4
    • Fighting historic enemy: +3
    • Crushing a rebellion: +2
    • Trade war: +2
    • Defending colony: +2
    • Defending land not historically connected with defenders: +1


If the government of the leading nation is a ...

  • Theocracy - 7+
  • Monarchy
    • Celestial Empire (China, Japan) - +6
    • Absolute/Despotic Monarchy - +5
    • Elective Monarchy - +5
    • Westminster Monarchy - +4
    • Feudal Monarchy - +3
    • Iqta' (Muslim) - +3
  • Oligarchy/Council - +4
  • Warlord/Tribal - +3
  • Free City (Holy Roman Empire) - +3
  • Merchant Republic - +2

Once the scores of this stage of the algo is found, advance onto the second stage. Here is an example of the Pre-War Algo:

  • Alliance I (Attacking)
    • Result: 34+
      • Pop: 28+
      • War Exhaustion: 0
      • Casus Belli: +3
      • Government: +3
  • Alliance II (Defending)
    • Result: 30+
      • Pop: 24+
      • War Exhaustion: 0
      • Casus Belli: +3
      • Government: +3

Battle Stage

This stage may be repeated up to six times, depending on the size and scale of the war. Note that in this stage, "Attacker" does not mean the nation that declared war first, but means the nation that is in the enemy's territory, attacking enemy cities or troops.

Army/Navy Size

If you are having trouble with army sizes, or your suggested army size is implausible, ask any moderator for the maximum army size you can field. Army size includes all allies and vassals on the same front.

  • 0.3+ Per 1000 Men 
  • 0.3+ Per ten Ships

Finding Maximum Army/Navy Size

  • Army
    • Feudal Nations: 0.0075 times entire alliance's population
    • Hordes: 0.01 times entire alliance's population
    • Non-feudal Nations: 0.02 times entire alliance's population
    • Naval-concentrated, non-feudal nations: 0.01 times entire alliance's population
  • ​Navy
    • ​Merchant Republic: 0.0018 times merchant republic's population
    • Naval-concentrated nations: 0.0000936 times population
    • Normal Nations: 0.000021 times population

NOTE: You can only send a fraction of your maximum military to any given front at a time. Be judicious of how much of your military you send to each front, as having too little military left could result in attacks of opportunity and/or revolts. During a Crusade, Holy War, or Colonial expansion, the fraction of the military must be very small (~ 25%) because not a lot of people would agree to fight such a long distance.


To find where land battle takes place, find the closest two major cities that is occupied by both sides. If the attacking player doesn't specify a plan, assume that the two armies will meet at a point between the two major cities.

  • Near a major religious site: +5
  • Near the center of government/state: +4.5
  • Near a city: +3.5
  • Near a major river or the coast with naval superiority: +3
  • Near a populated border: +2
  • Near a major river or the coast: +1
  • Near a desolate location far away from anyone: 0
Attacking-Assault on a City
  • Besieging a center of government/very well-fortified city: +8
  • Besieging a major religious site: +5
  • Besieging a major city: +4
  • Near a major religious site: +5
  • Near the center of government: +4.5
  • Near a city: +3.5
  • Near the coast or in a major river: +1
  • Far from any coast: 0
  • Near a major religious site: +7
  • Near the center of government/state: +6
  • Near a city: +4
  • Near a major river or the coast with naval superiority: +3.5
  • Near a populated border: +2
  • Near a major river or the coast: +1
  • Near a desolate location far away from anyone: 0
Defending-Assault on a City
  • Besieging a center of government/very well-fortified city: +12
  • Besieging a major religious site: +7
  • Besieging a major city: +4
  • Near a major religious site: +5
  • Near the center of government: +4.5
  • Near a city: +3.5
  • Near the coast or in a major river: +1
  • Far from any coast: 0

Great General or Admiral

  • General - +45 (Delegated via Event)
  • Admiral - +20 (Delegated via Event)

Attrition (Attacking)

  • Mountains: -10 (Lose 35% of Army)
  • Desert: -5 (Lose 8% of Army)
  • Tundra: -4 (Lose 6% of Army)
  • Jungle: -4 (Lose 6% of Army)
  • Along the Enemy Coast (Naval Only): -3 (Lose 4.5% of Navy)


RNG done by Unbiased, Non-involved Mod

  • -0 to -5

Here is the example algo for the battle stage. We'll only have one battle for this algo.

  • Siege of Alliance's II Capital
    • Alliance I (Attacking)
      • Result: 38.5
        • Army Size: 31.5+ (105,000)
        • Location: 8+
        • Great General: 0
        • Blunder: -1
    • Alliance II (Defending)
      • Result: 39
        • Army Size: 27+ (90,000)
        • Location: 12+
        • Great General: 0
        • Blunder: -0


Once the difference between the results are found (in this case, 0.5, and Alliance I lost), the difference is then subtracted from the loser's Pre-War algo score. Every one score difference in the Battle Algo means 20% of the loser's army is removed, and 6.6% of the winner's army is removed. For sieges, this is 30% losers and 10% winners for sieges. Army sizes are only reset after the war ends. If the battle is a dead draw, both sides lose 20% of their army/navy.

  • Alliance I Casualties (Losers)
    • 105,000 * 0.3 = 31,500 Dead
    • 105,000 - 31,500 Dead = 73,500 Men Remaining
  • Alliance II Casualties (Winners)
    • 90,000 * 0.1 = 9000 Dead
    • 90,000 - 9000 Dead = 81,000 Men Remaining

Cities Captured

If the battle was for the control of a city, and if attackers win...

  • Capital: -15 to loser's final score
  • Major City: -10 to loser's final score

Here is an example of the final algo.

  • Alliance I
    • Result: 18.5+ (34 - 15 - 0.5)
  • Alliance II
    • Result: 30+
  • Percentage: 162% in favor of Alliance II. This means that the war will continue into another year unless a treaty is signed.
  • In the event that one side has a negative score, you take |x|+1 and add it to both, where x represents the raw value of the negative result.

Victory or Defeat

A war will carry until a treaty is signed between warring nations, or an algo produces a final score difference of 200% (More or Less), at which point unconditional surrender is imposed. If the war is a player nation vs. nation with no player, then the player can force a treaty.

  • Treaty Tier 1 - 120-140% - Winner can only take the objective of the war
  • Treaty Tier 2 - 140-170% - Winner can impose somewhat larger territorial losses
  • Treaty Tier 3 - 170 - 200% - Winner can impose huge territorial loses, dictate loser's diplomacy and military post-war
  • 200%+ - Unconditional Surrender

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