Kingmakers units and officers
Your army is medieval even though you are not. A developer blog named six troop types planned for Early Access, each with a job and a counter; the later Gameplay Deep Dive describes recruiting from peasants up as a settlement grows. Neither list is final, and the two do not match exactly, so both are shown.
The troop types named so far
The store page lists archers, swordsmen, spearmen and cavalry. Swordsmen and spearmen being absent from the Deep Dive does not mean they were cut; the narration ends its list with “and more”.
The Early Access plan, in the blog’s words
“When Early Access hits, you’ll have six medieval troop types to recruit, which include: Swordsmen, Spearmen, Cavalry, Archers, Berserkers, and Men-at-arms. Most of which will be upgradeable up to two or three tiers to improve their proficiency.”
Redemption Road. From Steam announcement: Dev Blog #1, Meet the Troops You'll Command in Kingmakers
“Spearmen are effective against Cavalry. They can slow or knock riders off horses on impact.”
Redemption Road. From Steam announcement: Dev Blog #1, Meet the Troops You'll Command in Kingmakers
Recruiting, as the Deep Dive shows it
“At first, you’ll only be able to recruit poorly trained peasants, but as the settlement expands, you’ll field cavalry, archers, berserkers, men-at-arms, and more. Each has its own unique advantages on the battlefield.”
Redemption Road. Said in the tinyBuildGAMES video: Kingmakers - Gameplay Deep Dive
Recruiting happens from the strategy view, where you also build the settlement that unlocks better troops. That loop is laid out on Kingmakers gameplay explained, and the barracks, walls and defences themselves on Kingmakers base building.
Upgrades and losses
“Circling back to the skill tree, you can upgrade units through the skill tree by using holy relics collected during gameplay.”
Redemption Road. From Steam announcement: Dev Blog #1, Meet the Troops You'll Command in Kingmakers
“Hospitals can revive fallen members and restore the full squad, so long as they’re only partially wiped out, if the entire troop is gone, then you’ll need to recruit a new one.”
Redemption Road. From Steam announcement: Dev Blog #1, Meet the Troops You'll Command in Kingmakers
The blog also lists siege weapons and defences you place yourself: trebuchets, ballistas and archer towers.
Morale and officers
Soldiers are not scripted to fight to the last man. In the Deep Dive each one decides when to attack, hold or run, and officers are what keep them together.
“If you take down a high-ranking officer, this can cause a domino effect that leads to a massive retreat.”
Redemption Road. Said in the tinyBuildGAMES video: Kingmakers - Gameplay Deep Dive
“Enemy officers are valuable when captured alive. You can ransom them for gold, torture them for info, or execute them to boost your army’s morale.”
Redemption Road. Said in the tinyBuildGAMES video: Kingmakers - Gameplay Deep Dive
Asked whether enemies ever break and run, the game director added that the weapon matters as well as the officer:
“Enemy legions have morale, and you can make them retreat both by decimating the legion or targeting officers. Some weapons create more fear than others, and do more damage to morale.”
The blog called officers mini-boss fights, and the Deep Dive adds that promoted officers wear armour heavy enough to stop low-calibre bullets, which is why upgrades matter; the guns that answer that are on Kingmakers weapons and vehicles. One change since the blog: it said your own troops would not have officers because you fill that role, while the Deep Dive lists commissioning officers among the strategy-view orders.
Your army in co-op
In co-op, each player commands a separate army rather than sharing one. More on Kingmakers co-op.