Bellicomancy

Bellicomancy is a military discipline that focuses on the usage of magic in warfare. The discipline is practiced by most cultures in which practitioners are tolerated or even accepted in wider society.
== Overview ==
Magical warfare is practiced in many warring countries and usually boils down to the tactical suppression of the enemies practitioners, which invariably are a source of mass casualties in traditional armed conflict and require the adaptation of classical tactics.
== Damage and Incapacitation ==
This might be one of the most obvious applications of magic (fireballs, meteors, entire units falling asleep in the middle of battle), as well as the one with the most visible effects on warfare. Depending on the nature of the spells in question (specifically whether they're single- or multi-target), this turns spellcasters into either magical snipers or artillery. Sniper-casters will obviously focus on enemy Heroes, while artillery-casters will focus on entire units (either weak or strong, as mentioned previously). Important structures or infrastructure, such as bridges or catapults, might also be targets, especially for sniper-casters.
The presence of artillery-casters will drastically change what battles look like, since tight formations moving predictably are juicy targets. Who wouldn't love dropping a Fireball in a blob of foot soldiers? No more will there be gorgeous blocks of soldiers moving in lock-step, pikes at the ready. Instead, Everyone will spread out as much as is practical, making the front lines much more fluid.
It's difficult to imagine what battles like this would look like, since they were relatively uncommon in the ancient and medieval worlds. Organized formations were important for maintaining morale and discipline. It's a lot easier to prevent your soldiers from eagerly charging forward or fearfully fleeing when they're touching shoulders with their compatriots. Command and control is more difficult, too. The order for a unit to "withdraw, move to the right, and advance to envelop" is a lot harder when its members are scattered---possibly even mixed in with other units. Honestly, I've yet to see what this would even be like, so I don't have a lot of advice about how it would work in your worlds. I'd love any comments with insights!
Debuffs and Handicapping
The same dilemma of weak-vs-strong targets happens here. Should I hamper the platoon of imps or the four ice devils? Depending on the spells available, single-target casters may be forced to focus on enemy Heroes. The area of effect for many multi-target spells is centered on the caster, meaning that some may find themselves on the front lines if they want to be useful.
Summoning
The presence of summoners on the field is another massive game-changer. They can dramatically supplement the number, variety, and abilities of friendly forces. If the enemy is expecting a small number of melee-only infantry, the abrupt appearance of ranged creatures could be a fatal surprise. The effectiveness of this tactic depend on the prevalence of magic in your setting. If it's rare, your army may only be able to field a single high-level summon in a battle. If it's common, an entire spellcasting unit could summon an entire company of creatures.
Support and Healing
Support spells have the same considerations as handicapping ones: weak-vs-strong targets, Hero focus, frontline use of caster-centered spells. Healing has additional use in that it can be valuable outside combat as well. You might not have been there when a soldier was wounded, but you can still restore them to combat readiness. This is the first magical warfighting function where non-combat casters have the possibility to contribute.
Intelligence and Communication
Use of divination magic is a big one. Scrying and mind reading can make intelligence and reconnaissance operations far easier, more profitable, and more reliable. This means that magical countermeasures, such as illusions that fool scrying, will be just as valuable. Mundane reactions might also be used. For example, reading a commander's mind will make less of a difference if they've deliberately delegated decision-making to a subordinate.
The magical transfer of information among allies is incredibly useful. This could be done in combat---using Message to relay orders---or outside it---using Sending to deliver a truncated battle report. The speed and reliability of these communications makes planning and coordination far easier than real historical war.
Terrain and Siegecraft
These two areas are another huge force on the battlefield. Outside sieges, terrain manipulation can make a massive difference. The first army to arrive at a key location can create trenches, overlooks, waterways, forests, tunnels, and almost any other conceivable feature, making defensive operations significantly more customizable to a given unit's capabilities. Some spells that don't directly affect the terrain can still be used to shape its use. Glyph of Warding, for example, effectively creates a magical mine. A collection of them would definitely discourage a given avenue of approach. At the same time, holding onto a defensive location can be more difficult. Tunnels and ramps can bypass fortifications---you might even be able to just make a door.
Sabotage
There are two types of sabotage to be considered: equipment and personnel. A magically delivered plague or poison could wreck an enemy's ranks. Key equipment, from swords to ballistae, could be damaged or destroyed, disrupting their plans or making them completely unachievable.
Misdirection
Illusion and mind-control magic has the potential to be devastating. Single-target spells that manipulate Heroes can remove them from the fight, mislead those under their command, or make them fight for your side. Illusions could mislead scouts or cause diversions.
Logistical Aid
The application that is furthest from the battlefield is that of logistics. Despite this, it's another one that could make warfare almost entirely unrecognizable---at least behind the scenes. Let's start with the most basic considerations: food, water, and other bare necessities. In real life, there were two ways that armies sustained themselves---raiding and luggage trains. Of these, the rarer and more expensive was the luggage trains. The prospect of an army just carrying the supplies they needed (or having them trail behind in a "train") was difficult. It also left the supplies vulnerable to theft and sabotage. Instead, most armies just pillaged what they needed from their surroundings. This wasn't limited to outside lands, either. It was very common for soldiers to steal from their own citizens. Fun fact: frequently, soldiers returned to this lifestyle after wars and became bandits.
If magic is prevalent, these difficulties could be avoided. Food and water could be purified, enhanced, or created from thin air. Magic aids other areas, as well. Constructs could be made to carry supplies, or soldiers could be enhanced to allow them to carry more themselves. Broken or worn equipment can be repaired or replaced. Many of the logisitcal factors limiting real-world historical warfare to relatively small armies, short campaigns, and familiar climates can be ignored. The wealth of possibilities make the dungeon master's job significantly more interesting.
== How to fight magic users ==
Magic users are usually glass cannons and vulnerable, with subpar vision and senses.
Magic users must concentrate, and employ wards to keep off enemies when they are casting spells.
Weaknesses of magic users: iron blocks, absorbs and repels magic.
Some spells require movement to work
Countermeasures to magic in warfare
* Dismemberment portal
* Deathdrop portal: Useful against magically protected practitioners, and heavy units with magical protection. It is a portal to an area high off the ground. 
* Spy sky portal: Used to spy on troops, if spotted, projectiles can be fired into it if safe, otherwise false operations should be used. 
* Consent of death: soldiers that authorize a necromancer to reanimate them for military service. 
* Fireball present: remove armor and shields, troop formations must disperse, communication is paramount. Cover rushing and flanking tactics must be used. This of course unless magical shielding can be applied to protective clothing and shields. If the latter is the case, favor light clothing.  
* Disease cloud: Bubble breathing becomes mandatory
* Earthquake magic: If used to propulse units in the air, feather fall spells are to be used.
* Magical shield: usually either individual or formation based. The most common tactic is to attempt to disable the shield (by destroying the source device or practitioner) so that magical spells can be used to destroy the main formation. 
* Illusion magic: while large scale illusions are rare, they are devastating. If detected through use of falsehoods such as fake bridges during charges, false ground on top of pits, or making the enemy troops appear larger, the illusionist is a primary target, like with magical shields. 
* Fear spells: used to break morale, the practitioner should be a main target, and troops told to refocus on what is real and tangible. The apparition of such spells warrant activation of a magical shield
* Mind control: Usually banned, but warrant immediate usage of magical shields to eliminate the practitioner. 
* Daze: if Daze spells are detected, defensive positions are to be taken, and practitioners in the front lines should be dealt with artillery. 
* Mage hand: usually used to drop objects from up high, defensive positions are to be taken if detected and practitioners dealt with at range.
* Mount: Summons a horse for two hours, used for surprise cavalry charges, especially with charging foot soldiers, if used, resort to ranged attacks. Useful for lack of logistical needs, requires a spy network to detect suspicious nearby stables and subsequent sabotage. 
* True strike: since it guarantees a hit, retreat until spell is faded, resort to ranged covered tactics. 
* Charm person: usually stops combat from the allied side, use charm as well and resort to diplomacy with the opponents until it fades. 
* Invisibility: resort to colored liquid spilling to reveal the invisibles position, deal with heavy fire, since invisibility relies on stealth, usually the invisible unit will be lightly armed and armored. If the enemy cannot be detected, retreat until practitioners are dealt with. Used mostly for devastating ambushes, so attention to noise and detail is paramount if the tactic is known to be used by the enemy. 
* Silent image: used for fixed position guards and to give the illusion of strength, detect and ignore when in combat. 
* Enlarge person: Use large opponent tactics where the higher center of gravity is a disadvantage. 
* Conjuration: Eliminates need for most logistics, summoning food, water and other essentials, and as such practitioners should be eliminated as priority targets. 
* Healing: If detected, whether instant or regenerative, resort to killing blows or to wound the enemy enough to deplete magical reserves, practitioners should be priority targets. Once wounds are noticed once more (ie the enemy is noticeably less foolhardy in its tactics), resume normal warfare tactics. 
* Resurrection: Practitioners are priority targets, in the meantime diplomacy is to be favored. 
* Swamps: using fire magic can dry the swamp to ease travel for wagons. 
* Ice: Used for food preservation duty, creating bridges over rivers and sewers.
* Earth: dig tunnels, and have to keep them in place. 
* Water: Collect drinking water, splitting rivers to cross them safely.
* Teleporter: Warp in food.
* Clerical magic: Traps that detect disease and cure disease in hospitals. Trauma beds that cast cure wounds every minute. A table that creates food and water every minute to feed 15 people, capable of feeding 21600 people per day.
* Roads that make armies march faster
* Alarm spells
Category:Bellicomancy
Category:Unfinished articles
Category:Magic
Category:Magic Practitioners
Category:Tactics
Category:Military