Types of Units
Militia and Peasants
Militias are cheap, conscripted soldiers which historically have made up the bulk of medieval armies. Examples include peasants, slav warriors, and urban militia. They are cheap to train, have lower upkeep, and have low requirements to build. The fighting quality of militia type units varies from average to terrible, depending on the units. Most are lightly armed and armored and serve well as support units to nore professional soldiers which make up the core of the army. Militia type units are most common in the early part of the early era, when most factions are bulking up their first armies and gradually they are replaced by stronger and more powerful units as the years go by.
Militia are good for garrison duties in safer provinces. Having an army in the province boosts loyalty but it does not matter what quality the units are, peasants count as much as knights in terms of boosting loyalty.
Militia can serve a use in battle as well, just by sheer numbers. Outnumbering the enemy gives troops a moral boost and lowers the moral of the enemy, several units of peasants coule double or tripple the size of an army and tip the balance in favor of victorty. Militia units also are quite expendable and can be used to soak up missle fire, serve as fodder for enemy units and most roles which any warm body will do.
Beware the low moral that most militia units have. They are often the first units to route, and that lowers the moral of other non-elite, non-disaplined units in the army, sometimes causing a chain reaction leading to the loss of the battle.
Skirmishers
Skirmishers are lightly armed, fast troops. They typically have little to no armor, and are armed with javalins or short bows. Their job is to pester slower enemy infantry units, causing casualies and disrupting enemy formations. They are not very strong in melee, but usually are tough enough to kill archers or other skirmishers and sometimes are useful as flankers.
In battle skirmishers usually start ahead of the main battle line and fire on the enemy as they approach. This forces the enemy to either ignore them and take the casualties, or to divert troops to drive the skirmishers off -- possibly spliting up the army and causing breaks in the line. Skirmishers are fast enough to retreat behind friendly infantry until battle is joined. They can then circle around enemy lines and fire into the rear.
If the battle is won skirmishers can chase down routers since they are faster than most infantry.
Light cavalry is the bane of skirmishers, they are quick enough to run them down, and usually powerful enough to decimate a unit of skirmishers caught in the open. Skirmishers will also die when fighting heavy infantry, like swordsmen or shocktroops, head on and should run.
Spearmen
Spearmen include both true spearmen as well as halbadiers and pikemen.
Swordmen
Shocktroops
Shocktroops are strong, offense-oriented attack infantry. Their job on the battlefield is to break enemy formations and cause as much carnage as possible. They are heavily armed but often lightly armored, with high attack and charge values and often an armor-piercing attack. They are used either in a frontal attack against the enemy lines, or as flankers marching around the enemy to charge from the rear. Shocktroops are expected to take terrible casualties and are by nature somewhat expendable. Examples of shock troops are Varangian Guard, Vikings and Ghazi Infantry.