Attacking other realms and defending your realm is the most important part of Realms of Mayhem. If you want to protect your land and acquire new land from others, you must have a strong army (and fleet after researching Ship Building).

There are lots of unit types in Realms of Mayhem, and each of them has different advantages & disadvantages. According to these, you should find your preferred units and produce them. Focusing on producing similar types of units is beneficial for military masteries.

Military masteries become available as a research after researching Battle Tactics and fighting some battles. Mastery types appear according to your unit types. For example if you have mostly axemen in your army, Axe Mastery will become available sooner than other mastery types. When you research a mastery, its bonus will be applied to your units immediately.

In order to train a new division, you need resources, weapons (generally), humans and turns. When a division is trained, it will be put under division pool. Divisions under division pools will not join any fights until they are assigned to an army or a fleet. So, if you want to defend your realm, you should form armies/fleets and assign your divisions to them. But if you want to keep your units safe, only thing you should do is to keep your divisions in division pools.

Military units has wages that are deducted from your gold every turn. A large army or fleet may be too bad for your economy, so always keep an eye on your military expenses. Otherwise you may need to disband your divisions due to economic reasons.

Units' abilities do not differ whether in defence or assault. Meaning that you can attack or defend with any type of units efficiently.

While defending, your units can get bonus from defensive walls. Castles do not give your units any defensive bonus, but they reduce the land lost when you lose a battle in your realm. More properties of castles will be explained in Castles & Sieges.

Attacks can only be made against Lords within certain point limits. Their points can be at most 1.25 times of your point, or your point can be at most 1.25 times of their points. Sending reinforcements has a higher point range limit, in which the point multiplier for limits is 2 instead of 1.25.

Whenever you win a battle, your people's morale will increase for a period of time. And when you lose a battle, your people's morale will decrease. But don't worry, morale decreases are smaller than morale increases and its effect on your economy will be smaller.