Peasant Levies (All): In almost every time period, somebody had the bright idea of taking the lower class, arming them with inexpensive weapons (more for moral purposes than in the hopes of them killing anybody), and herding them in the direction of the enemy. Peasant levies tend to be terrible fighters and chain routes can occur, causing a significant portion of the peasants to run away. Peasant levies are the economically cheapest units, but also the most population expensive.
Legions Heavy Line Infantry(Antiquity and medieval): The legions consist of well trained soldiers carrying broad shields and short swords. Legions always fight in line formations and generally have an advantage over swordsmen in close combat and are more maneuverable than phalanxes. Experienced legions can sometimes even take phalanxes head on. However, legions generally suffer from a lack of suitable weapons to deal with heavy cavalry such as cataphracts or knights. But this, and the legion’s high price, are little comfort to the infantry they slaughter.
Phalanx Army Heavy Line Infantry(Antiquity): Phalanxes are 16x16 squares of men carrying long pikes to prevent enemy swordsmen and cavalry from getting close. Phalanxes are excellent units to use against medium infantry because for anything but an experienced legion or another phalanx, a head on attack is suicide. Phalanx formations can stretch for miles and provide nothing but a row of spear tips for the enemy. Little opportunity to outflank. However, phalanxes are generally slow and must be on perfectly flat terrain to fight effectively. This means that in a dense forest or a city, phalanxes lose formation and can be killed by infantry like swordsmen or run down by cavalry. A phalanx that is outflanked or loses coherent formation is a dead phalanx. The upside of a phalanx over a legion is its much lower price.
Armored Infantry (Medieval, Renaissance): Armored Infantry consist of elite knights wearing full plate armor and fighting on foot with heavy weapons such as broadswords, maces, and axes. Since they wear plate, they are incredibly expensive to train and are only useful as shock troops. They can be invincible in a melee, but crossbows, ballistas, muskets, and spears generally make quick work of armored infantry.
Medium Infantry (All): Lightly armored swordsmen and axmen existed since the practice of metal working began. They are generally a solid army choice and are far cheaper than any of the other infantry choices. Medium infantry is never effective against the fronts of legions or phalanxes, but they are usually better than both if the legions or phalanxes break formation.
Hoplites Heavy Infantry(Bronze and Antiquity): Hoplites are composed of spearmen in a packed shield wall. One man thrusts with his spear from below while the man behind him thrusts his spear from above. This creates a deadly melee zone, effective against most infantry formations. The Hoplites are great against medium infantry when in a line and can put up a fight against legionnaires. However, they can easily be destroyed by phalanx armies, who have longer spears. Like all line formations, they can easily be devastated by cavalry or medium infantry once they lose cohesion.
Light Infantry (Bronze, Antiquity, and medieval): Light infantry is always made up of unarmored (or lightly armored) loose formations meant to cause chaos, weaken the enemy, and take advantage of any weaknesses. Light infantry cannot face off heavy or medium infantry head on and will be annihilated by cavalry unless equipped with spears. Nonetheless, Light infantry are vital for heavy infantry to do their job unhindered.
Skirmisher Light Infantry (Bronze, Antiquity, Medieval): Skirmishers are light infantry who are given javelins and act as supporting units for line formations or can tire out enemy heavy infantry on their own. Skirmisher units should be careful not to be near medium or light infantry or cavalry.
Pikemen Heavy Line Infantry (Medieval, Renaissance): Pikemen have the single duty of protecting infantry against charges from Heavy cavalry. They can stop even the heaviest of cavalry charges. In Renaissance armies, they can also be positioned around the musketeers to protect them from cavalry and infantry assaults (Known as 'pike and shot')
Slinger ranged light infantry (Bronze, Antiquity): Slingers are men who are brought up learning to use the sling, a primitive but very effective weapon. The sling is a long pouch meant to hold a round stone and let the user throw the stone at a high enough velocity to break bones. While slings will do little to plate armor, they can be very effective against light and medium armor.
Archers Ranged Light Infantry(Bronze, Antiquity): Arrows were always potent weapons on the battlefield, especially against lightly armored infantry and cavalry. Archers are great for taking out light and medium infantry from any angle, and even heavy infantry from the flanks. Light and medium cavalry can also be destroyed by accurate arrow volleys. Archers are generally not armed and will be steamrolled by any infantry or cavalry.
Longbow men Ranged Light Infantry(Medieval, Renaissance): The Longbow men are like archers, but are also able to effectively attack heavy infantry and cavalry. They are, however, difficult to recruit because only the strongest of men are capable to shooting longbows.
Crossbowmen Ranged Light Infantry (Renaissance): The Heavy Crossbowmen were invented to deal with the threat of plate armored cavalry and heavy infantry. They have a slow reload time and are expensive, but are a cheaper alternative to the arquebus armed infantry.
Musketeers Ranged Medium Infantry(Renaissance): Armed with the Arquebus, musketeers have no equal for dealing with heavy infantry and cavalry… at range. They are generally armored in a cuirass, which offers good protection against other musketeers and archers in melee. However, musketeers are extremely vulnerable against anything else in melee, and can be outshot by archers (Who fire 12 arrows for every musket volley).
Light Cavalry (Bronze, Antiquity, and Renaissance): Light cavalry is ideal for chasing down light infantry, archers, and routing units. However, light infantry should never be used against medium or heavy infantry or medium or heavy cavalry. The only time light cavalry should engage medium or heavy units is with a flank charge when the enemy unit is fighting enemies in the front.
Light Lancers (Bronze, Antiquity, and Renaissance): Light lancers are unarmored cavalry, just like light cavalry. However, they are armed with spears or lances of some sort, which gives them a devastating initial charge. Even light lancers can be used as shock troops against medium infantry. However, the use of a lance over a sword means that light lancers caught in a melee will be quickly cut down. The strength of all lancer cavalry lies in their charge.
Horse Archers Ranged Light Cavalry (Antiquity and Medieval): Archery and cavalry have always been the most dangerous elements on an ancient battlefield. Horse archers combine the ranged killing power of the bow with the speed of a mount. This way, they are able to not only get into prime firing positions, but also evade melees with infantry and heavy cavalry (although light cavalry can be a major threat). They are very potent, especially when being used in an all cavalry army.
Medium Cavalry (Antiquity, Medieval, and Renaissance): Cavalry armored in chain or a cuirass and armed with a sword is excellent for dealing with light or medium troops and light cavalry. Medium cavalry is not as fragile as light cavalry and can engage in frontal attacks. Medium cavalry tends to be slightly expensive and difficult to recruit.
Medium Lancers (Antiquity, Medieval, and Renaissance): Medium Lancers are more armored than light lancers and can perform outstanding charges against medium and even heavy infantry. Like light lancers, however, they will be killed in a grinding melee, so they must only be used in cycle charges.
Cataphracts (Antiquity, Medieval): Cataphracts are an interesting blend of medium and heavy cavalry. Their armor is made out of heavy chain or overlapping plate scales, giving the rider and horse much better protection that a cuirass or hauberk could ever offer. Cataphracts can engage most infantry head on and win without problems. Even legions suffer from an inability to repel Cataphract charges effectively. However, Cataphracts also lack the protection of heavy plate armor heavy cavalry uses. Only their medium cavalry speed saves them from being cut down by heavy cavalry. Cataphracts are pretty expensive.
Heavy Cavalry (Medieval, Renaissance): Heavy cavalry is plate armored and used to add a shock element to an army. While heavy cavalry does not cause an overwhelming amount of casualties, even a bloodless charge can be terrifying enough to cause a low moral unit to route. Just the presence of enemy heavy cavalry causes fear. Heavy cavalry is generally the most expensive unit (except bombards) to recruit.
Heavy Lancers (Medieval, Renaissance): Heavy Lancers, usually plate armored knights, are the best shock cavalry possible. Even a frontal charge from heavy lancers will break most infantry formations. Sometimes, even a feint charge may cause the enemy to lose their head and route, making them easy targets for cavalry. However, Heavy lancers should never be charged into pikes or phalanxes, and should never end up in a melee against heavy infantry or cavalry.
Doppelsoldner Heavy Infantry (Renaissance): Devised as a way to counteract pikemen and phalanx formations, the Doppelsoldners are equipped with halberds and two-handed swords that can chop the tips of pikes off, allowing them to march into a pike formation and lay waste to the men inside of it. Their two handed weapons, however, render them vulnerable to ranged fire, and their lack of armor to allow for mobility also makes them targets without proper support.
Spear Militia Medium Infantry (All): A quick, cheap, and easy method of raising spearmen to defend against cavalry revolved around using peasants raised into a militia and trained in the use of the spear. This provided a cheap, albeit sometimes ineffective, method of warding off cavalry. When put into a Schiltrom Formation, however, the Spear Militia become surprisingly hardy. Don't put them against anything more dangerous than a stiff breeze if it doesn't deal with cavalry, however.
Skirmish Cavalry (Antiquity, Medieval): Like their brethren the Light Cavalry, Skirmish Cavalry are quick, fast, and agile, but unlike them, they are equipped with javelins. They have less charge capability than the average cavalry member, but make up for it by being an extremely mobile force that can break up and tire out formations through their javelins.
Bombardiers Ranged Infantry (Renaissance): Using unique and sometimes dangerous gunpowder bombs, Bombardiers throw these small grenades at enemies, causing untold damage and catastrophe, not to mention morale damage. However, they have no real weapons other than their grenades, and there is a chance that the grenades may explode, setting them on fire.
Galleass (Medieval, Renaissance): A further development of the Galley, the Galleass was designed to be used with both sail or rowing, allowing it to keep an excellent amount of mobility in bays, harbors, or other such close to land arrangements. In addition, it is little more than a platform for siege weapons, and its firepower is matched by very few ships on the sea. Unfortunately, the Galleass is big, heavy, slow, and doesn't sail well at all on the open sea.
Pistolier Ranged Cavalry (Renaissance): The first foray of most nations into the idea of using gunpowder weapons while mounted, the Pistolier is a lightly-armored, skirmishing unit that wields a brace of primitive pistols in battle. Despite the obvious advantages of a cavalry unit using pistols, the pistols remain woefully inaccurate, hard to reload, expensive, and unreliable. In addition, the Pistoliers can be easily run down by light cavalry or even horse archers, being relatively unable to defend themselves after discharging.
Ballista (Antiquity, medieval): The ballista is a formidable long range artillery piece designed to punch holes in enemy shield line formations. It is a great but expensive weapon to have when fighting an enemy army which is based on formation.
Catapults (Antiquity, medieval): The catapult is a siege weapon for bringing down walls or for creating gaps in enemy line formations. They are slow and make moving with an army difficult.
Bombards (Renaissance): The bombards are large, heavy, cannons used only for siege warfare. They can easily bring down early period walls, but are of little use on the battlefield.
Cannon (Renaissance): The cannon is mostly an anti-infantry weapon. This small cannon is capable of gaining a huge body count when firing at dense infantry formations, because a round shot will go through up to twenty bodies and canister shot will spread out like a massive shotgun.