I've said this before...but here it isagain..

To see the difference in difficulty levels as far as battlefiled fighting goes, do this:

1. Select Custom Battle from the menu, select the Easy difficulty. Buy yourself one unit Honor 5 monks.
2. Also, buy one unit of Honor 5 monks for the enemy. Make sure you have selected a advantageous battlefield.
3. Attack/Defend, just make sure you have the advantage of height.
4. After a while, you should win the battle with maybe half your unit left; theenemy may be all dead or may have fled.
5. Now, do this again, but on Expert. Repeat the battle.
6. You should still win, but will probably have only 1 or 2 monks left. You probably had to kill the entire enemy unit.

that's the difference. The enemy gets harder to kill, or is less likely to die.