Ready to go to war in Crusader Kings 3 and claim your enemy's territories for your own? Here's how to declare war and reap the benefits.

Crusader Kings 3 Guide: How to Declare War

Ready to go to war in Crusader Kings 3 and claim your enemy's territories for your own? Here's how to declare war and reap the benefits.
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You’ve gotten married and produced an heir. Now it’s time to expand your realm. One of the quickest ways to gain new territory is by conquering other territories, but war in Crusader Kings 3 isn’t as simple as just sending an army somewhere. There are a few steps you need to take in order to actually get your troops going and declare war.

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Understanding how wars work, and how declaring war works, in Crusader Kings 3 is vital to your success and your line of succession. If you’re wondering how to declare war, you’ve come to the right place. Here’s everything you need to know.

How Do I Declare War in Crusader Kings 3?

A cursor hovering over a liege's coat of arms to see information about a current war.

The actual mechanics for declaring war are fairly simple, and there are two main ways to do it.

Join Another Ruler’s War

If you’re a smaller ruler in a large empire, you’ll probably notice your liege going to war quite a bit. Look at the bottom right of the screen to see any ongoing wars.

If your liege or ally is in a war you can “declare war” by:

  • Clicking the icon.
  • Right-clicking on the portrait of your liege or ally.
  • Under the Diplomacy section, clicking Offer to Join War.

This is often a good way to accumulate some gold, prestige, and favor if you have a decent military but no reasons to declare war on your own.

Declare War on Your Own

You can also declare war directly on certain characters. To do so:

  • Right-click their portrait.
  • Click Declare War.

You will then choose your Casus Belli and the war will begin. If the Declare War option is grayed out, it’s because you have no valid Casus Belli. So, how do you fix that?

What is Casus Belli in Crusader Kings 3? 

The council menu showing the various council members, and the bishop who can fabricate claims.

The term Casus Belli literally just means “reason to go to war.” It’s the justification for raising troops to try to conquer or kill an enemy. There are several different Casus Belli options in Crusader Kings 3, and they can be triggered in a variety of ways.

One of the most basic Casus Belli options is to send your religious head to an area to Fabricate a Claim there. This is especially useful for tribal rulers who don’t have a ton of power or sway yet, as their options to expand their realm are usually limited. We have a whole guide on Fabricating a Claim that you can check out right here.

There are a lot of different Casus Belli available throughout the game. They often come up through alliances, religion or culture differences, or claims on titles, either pressed or unpressed.

As you become more powerful, you’ll often be able to declare wars of conquest, so keep an eye out for new areas to take over.

Rally Points and Troops

A map of forests and rivers showing a rally point for troops.

Once you’re at war, you’ll need to get your troops moving. To do so, hit the “F3” key or look on the top right side of the screen for the red shield icon. This brings up your Military menu.

The first thing you’ll need to do is set your Rally Points. Troops will spawn at the rally point nearest to their home holding, so Rally Point will usually do. Just make sure you set it near the area they’re marching to so they can get there quicker.

Also, you cannot raise troops in a holding that an enemy currently occupies, so you may have to move a Rally Point if you are responding to an invasion.

On the military menu, click the Raise All Armies button to rally your troops. They will take up arms and be ready to battle.

Men-at-Arms, Mercenaries, and Raiders in Crusader Kings 3

The mercenary menu showing the mercenary armies a player can hire for gold.

A few notes on these specialty troops you’ll use when declaring war in Crusader Kings 3


Men-at-Arms are professional soldiers, as opposed to levies, which are citizens who take up arms. You can create Men-at-Arms regiments based on your rank as a ruler and your military skill, and each can be classified as a certain type of troop.

Some regiment examples and their creation costs include: 

  • Light Footmen (50 gold)
  • Bowmen (75 gold)
  • Light Horsemen (115 gold)
  • Pikemen (100 gold)
  • Armored Footmen (125 gold)
  • Onagers (80 gold)

Each category will also include what a unit’s full and unraised maintenance costs are, as well as the units they are most well suited to fight and what terrain types they are best used for. 


Mercenaries are also professional soldiers, but you must hire them. They are usually extremely high quality and can help turn the tide of a battle, but they cost a lot of money.

By clicking on the Mercenaries tab in the Military menu, you can see a list of mercenary armies, as well as their affiliations, soldier count, soldier type, and cost. 


Raiders can be raised to invade territories you aren’t at war with. This is a nice way to earn some gold and prestige, and maybe even take some valuable prisoners.

However, only certain types of leaders (tribal being the main type) can actually raise raiders. Raiding a holding also makes it unavailable to raid again for a set amount of time.

That’s all you need to know about how to declare war, raise armies, raid, and rally troops in Crusader Kings 3. Go forth, noble leader, and may all quake before your might! You’ll need to know how to raise tons of money from the populace; here’s how to do so quickly. You’ll also want to know how to replenish your all-important Levies. For more tips on Crusader Kings 3, check out more strategies here.

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Jordan Baranowski
Jordan has been gaming and geeking since he was a wee lad. He is a freelance writer and content creator, contributing to AMC Theatres, SVG, Looper, and Feast Magazine, among others. Follow him on Twitter for article updates and Instagram for (mostly) pictures of food and animals.