For article on combat and the flow of battle in Crusader Kings II go here: Combat & Battle or Combat and Terrain
There are certain tactics you can employ to improve how well you do in war. Many of these tactics are common sense, but I'll mention them anyway.
One tactic that is useful for reducing how annoyed your vassals get with you, is raising troops from a minimal number of direct vassals. If you only need the troops of a single vassal to fight a war, only raise those troops. This vassal will now be the only one getting annoyed at you, while the rest will continue to be happy. The other vassals' levies can then be raised later if ever needed. If you're rich enough to support it, you can also consider using only your own levies, as then no one will be getting annoyed with you.
Second, you can use the bait and switch tactic. You offer up a small, easily beatable target to the enemy so that he attacks, then immediately once combat has started, you send in your larger army from a province away, thus winning the battle easily. This means you won't have to spend half an eternity chasing the army down, instead being able to quickly destroy it in a single or a series of decisive battles.
Third, if it is obvious you'll lose to an incoming enemy due to either a lack of troops or a lack of morale, consider sacrificing a small number of men to let the rest escape. Let a few men remain while the rest go to another province where they can hopefully recover or merge with a larger army. Make sure you leave more than 1/25 of the enemy army, as anything less than this will be destroyed instantly, and as such will not slow the enemy's advance down.
Fourth, you could try to bait the enemy into a province where they'll take attrition. Using an army smaller than theirs you can continuously pull back, leaving them in a province where their units will slowly die. Only works against large armies.
Fifth, if you can target a part of an enemy's army while it is split up, do so. While you might not be able to defeat the entire enemy army at once, you're likely to be able to defeat half their army, and the rest is then easy to mop up.
Sixth, always go for the wargoal first if you have the opportunity. Occupying wargoal holdings will give 75% more warscore, and once you hold every wargoal holding you'll slowly get warscore. This can ensure a quicker victory, and as such less losses to combat, sieges, and attrition. On the other hand, never let the opponent take the entire wargoal if you are the one being attacked, for the same reasons. Do note that the moment one side reaches 100% warscore, it can force victory.
Seventh, you should almost never split your army up into pieces smaller than the total size of the enemy army. If you do you risk losing a large part of your army, and being reduced to a position where you can no longer fight back. If you have a really good reason to do so, go ahead, but make sure you keep the rest of your army close.
Eight, if you're a coastal nation, utilize the mobility ships give you. You can transport units much faster by ship than on land, which can enable you to quickly strike at isolated enemy armies, then retreat back to sea.
Ninth, avoid attacking across rivers and into hills if possible. You'll get a moderate combat penalty, which could make a major difference. These penalties don't matter much if you outnumber the enemy by a lot, though.
Improving Your Army
There are five ways to improve your army:
- Construct army buildings, covered in further detail here
- Research technology, covered in further detail here
- Strike the right balance between levy law and vassal opinion, covered in further detail here
- Improve your commanders
- Make your vassals happy
As the rest is covered in other installments, I'll focus on the last two points.
The first, improving your commanders is relatively simple. First, you need at least Limited Crown Authority, as that enables you to assign commanders. Once you have that implemented, you can invite high-skill commanders to your realm, either via inviting them normally and giving them some land or a councilor position, or by marrying them into your realm. Then you just have to make sure that the best possible commanders are appointed before any major battle. This could improve the damage your army does by several percent, making it easier for you to win battles, and reducing your losses. It will also decrease how much attrition you take, and you'll also get someone great for the Marshal position. This tactic is seldom necessary for a large realm, as you'll then generally have good commanders available already, just make sure to assign them.
Second, you can make your vassals happy. As mentioned in the installment on levies, the higher your vassals' opinion of you, the more levies they'll provide. As such it can be a good idea to send out gifts and honorary titles before raising levies so as to maximize how many you can raise.
Summary
By outmaneuvering or overpowering the enemy you'll be able to win most battles, and eventually the war itself. Overall my tips are these:
- Construct buildings to increase the size of your army. More detail here
- Research relevant tech, it can give you the edge you need. More detail here
- Appoint good commanders. Gain good commanders through marriage and invites
- When hiring mercenaries, go for heavy infantry and cavalry
- Keep your vassals happy
- Strike the right balance between levy law and opinion. More detail here
- Don't raise more troops than you need
- Ambush the enemy if possible
- Slow down the enemy's advance by sacrificing units if needed
- Go for the wargoals first
- Go for 100% warscore ASAP
- Divide and conquer
- Utilize the mobility ships give you
- Avoid attacking across rivers and into hills
contributed by Meneth