How to calculate an attack:

First of all, you need to get information of your desired target. There are three operations that will give you information about other provinces military.

1. Crystal Ball (spell) - it will give you EXACT information about the targets military (except humans and faeries who may have cast "illusionary forces" to deceive Crystal Balls)

2. Spy on Military (thievery operation) - it will show you how much of your targets military is away, and for how long. But this is only an estimation! The more thieves you send, the more accurate - send 1 thief for rough estimation, send 100 thieves max! It won't get more accurate than that!

3. Survey (thievery operation) - it shows you the targets building strategy. Check for guard stations that may reduce your grabs and for forts which give your target higher defense!

4. Kingdom Stance
if your kingdom is in "fortified" stance, you have 15% lower offensive strength!

5. Plague
if your target province has got the Plague, it's defense is reduced by 15%

Now you have all the information you need! You just have to do some maths before you attack, or you will fail! (Or you just use the Utopia Angel Crystal-Ball formatter who does all the maths for you!)

Basically, what you do is that: Calculate the total defense points of your target by using the table in The Military.

Probably your enemy has cast the spell "minor protection" which will increase his defense by 10%.

Next you do similar calculations for your offense: number of offense points, add +1 for every horse you send into battle, should you cast bloodlust (a spell for Orcs, Avians, and Faeries only), add +10% to your offense points. And you may consider hiring Mercenaries if you have enough gold and you think it's necessary!

Now you can decide if you want to attack - there is a random factor in battle, so you have to send MORE offense points than your target has defense points. Remember to leave enough defense at home, so you won't be counter-attacked so easily!