That's war baby! [D20]

Recently a friend asked for help to design a war system for his homebrew dnd 5 campaign, and i'm a bitch for homerules on the fly.
Before going down, i want to clarify that this homerule is not intended to reproduce a 1:1 scale of war, but to integrate storytelling and already existing rules where there may be something missing.

So no more talk, here's the refined WYP:

• Army description:
  Each army unit must have
• Generic type of movement (land, sea, air):
  If they have more than 1 type of movement, split the units in whatever movement you chose to use mainly.
  
  (Galleons are comprised of sailors, but are still considered a sea unit, not a land/sea unit. Dragons and their riders would be considered an air unit, not a land/air unit. Different species of quadrupeds controlled by a druid would be seen as a land unit, not as a separate ones).
• Wants:
  Each time the unit fights for something that isn’t its objective, the unit starts a clash with a lesser quality (d8 becomes d6, d4 becomes 1).
  This is a way to encourage players to not think of the army as another ability they have gained, but as a collection of individuals that want to reach a set goal. The more specific it is, the better.
• Weakness:
  What can be used by its enemies against it, and that can reduce its quality dice by 1 (d8 becomes d6, d4 becomes 1) when exploited by them in combat. The unit gets a weakness based on their nature. The more specific it is, the better.
• Player characters and Aces:
  Each player can have under his control whatever number of generals/commanders/captains/whateveryoucallthem (for commodity we'll use the term Ace), as long as the sum of their levels is equal or lesser than their character level (Ex. Caius lv.9 commands 2 Aces: Brutus lv.5 + Tiberius lv.4, for a total of 9).
• Aces can be whatever NPC that for any number of reasons decides to take the task (And as such, may be trustworthy, or betray you based on the relation with the character), so the last word goes to the GM. Aces have their own stats as every NPC.
• Player character can be their own Aces but they must completly commit to the army or it will not act, and it may even disperse.
• The minimum level for a player character to control an Ace must be lv.4.
• Size:
  Each unit starts with 1 dice at least in it.
  Each army unit can have as much dices in it, to a max. of the Ace lv. (So an unit controlled by an Ace 4 can have no more than 4 dices in it). 
  An army unit gains and loses dices with the story, by defeating strong enemies and being defeated, gaining respect and losing it allies, convincing others to join their cause with money, strenght, or pacts. You get the idea. 
  The sheer scale of the unity is as follows:
• = 1: You won't even consider it an army (Ex. A bunch of bandits)
• = 4: You can count each element in it (Ex. Squad)
• = 6: You can see it from afar (Ex. Troop)
• = 8: You can't see where it ends (Ex. Company)
• = 10: You know of its arrival days before (Ex. Cohort)
• = 12: You know for sure that this is the last battle (Ex. Legion)
• Quality:
  Each army unit is represented with a dice, starting with a d4 and ending with a d12. The dice represents the average quality of the members of the unit based on the setting and the type of unit you decided it to be, and should not have a specific definition, but to get an idea here’s some examples:
• d4: rookie soldiers, zombies, brigs, or dragon wyrmlings
• d6: experienced soldiers, skeletons, fluts, or young dragons
• d8: elite soldiers, ghouls, frigates, or adult dragons
• d10: veteran soldiers, wrights, galleons, or old dragons
• d12: heroic soldiers, liches, line ships, or ancient dragons
• The minimum level for an Ace to control a unit must be lv.4.
• Each Ace  level must be equal or greater than the size dice of the unit. So a d4 unit requires at least an Ace of lv.4, and a d12 unit requires an Ace at least lv.12.
• If for any reason the Ace has a lower lv. than the quality/quantity, after each clash reduce the size dice of the army by 1 until it's again equal or major than the quality/quantity dices (The inadequacy of the Ace convinces some to mutiny, other to flee, others to betray...).
• Turns and Movement:
  Each army gets 1 movement per turn. Usually 1 movement means 1 hex, and 1 turn means 1 day, but  it can be whatever you have decided to use in your setting (1 mile, 1 half day, 1 whatever).
• Tactics:
  Each army has a number of moves, called Tactics, equal to the size dice of the unit (d4 = 4 moves, d6 = 6 moves, and so on).
  
  It’s implied that every unit is capable of at least 4 basic moves, and the other ones can be chosen each time the quality increases or decreases (Quality of the members composing the unit decides if they're capable to make some more complex maneuvers, or if it's even possible to make them with such resources). Every unit is composed of many individuals with different experiences and abilities, so if there’s enough members that share a skill, they can use it as a whole. 
  Moreover, 1 of those tactics must be something linked with the Ace in command. Some example of basic moves can be:
• Frontal attack: Enemy army loses 1 more dice.
• Settle: For 1 turn you will recover, and improve the quality of 1 dice you will roll your next turn. If you get attacked before your next turn, decrease the quality of 1 roll.
• Defend: Protect 1 dice from being lost from 1 enemy attack.
• Retire: Pay 1 more dice, but get away from the fight and don't lose any more dices.
• Duel: Before starting the clash, the two Aces duel like any other NPCs. The winner of the fight launches 1 dice as if it’s improved (1d4 > 1d6, 1d12 > auto 12). The loser launches 1 dice as if it’s worse (1d8 > 1d6, 1d4 > 1 auto).
• Forced march: Army can make 1 more movement but loses 1 quality dice until recovery.
• Diversion: Army lets another allied army in the fight get the use of 1 more tactic.
• What skill would siege weapons give? Barbarians? Mages? Rocs? Galleons? Use the rule of +/- 1 dice, and let me know.
• Clash between armies:
  When two or more armies clash, they launch as many dices as their size permits. Once decided, roll the size dices + the lv. of the Ace in command (That's a crude count of the Morale of the unit). Once those dices are used, they can’t be reused until the army rest, except if a special ability says so. Like in Risiko, compare the dices with the ones of your enemy:
• When a dice gets the max. result (Ex. 6 on a d6), it explodes and you can launch another separate one.
• For each dice an army wins, it can use 1 Tactic.
• Dices lost, are forever discarded.
  Dices won, get back in the reserve after the clash, when the army has rested.
• Write down the tactics you want to use in secret once you have established how many dices you have won against your enemy, then show together each other your lists, and apply the effects.
• When an army loses all its dices, it begins decreasing its quality dices instead.
• An army surrenders or gets defeated when its quality dices gets lower than a d4 for whatever reason (defeat, or general defection).
• A clash usually takes 1 turn, and then each Ace decides if keep fighting, or retreat and move away.
  There may be scenarios in which both armies want to retreat and return home, and ones in which an army retreats while the other chase it.
• Individuals against an army: Individuals must be treated as a single army, with quality 1, size 1, and morale equal to their lv. or CR (The higher between them). So a peasant or a fisherman boat can still try to attack and be crushed, but an high lv. group of Player character, or an high CR enemy, can still be a challenge.

Army examples:

Ace:	Necromancer Gustav lv. 15
Unit:	Undead army
Movement:	Land
Wants:	Destruction
Weakness:	Sacred
Size	10
Quality	D12
Morale	+15
Tactics
Frontal attack

Ace:	Desert barbar Cervantes Yrafel lv. 8
Unit:	Fire elementals
Movement:	Land
Wants:	Freedom
Weakness:	Cold
Size	5
Quality	D4
Morale	+8
Tactics
Frontal attack

Ace:	Sky knight Morzan lv. 12
Unit:	Dragon knights
Movement:	Air
Wants:	???
Weakness:	Necrotic
Size	10
Quality	D10
Morale	+12
Tactics
Dive attack

Ace:	Cassius Ternan lv. 16
Unit:	Soldier legion
Movement:	Land
Wants:	Law and order
Weakness:	Magic
Size	15
Quality	D12
Morale	+16
Tactics
Defensive attack

I hope you liked it, feel free to suggest how it can be improved.

Sources used: 7th sea 2nd ed.; Patfinder (mass combat system); D&D 5 homebrews; Gorgonstar - Titan rules; and most importantly this blog Titan scale mass combat