Check out the Kings of War rules and army list download here.
ALIGNMENT
All army lists have an alignment; Good, Evil or Neutral. It is possible to include units in your army from multiple army lists, as long as the army lists have similar alignments. Neutral army lists can align with either Good or Evil.
For example, you could have an army that consisted of both Undead and Orc units, but you could not have an army with both Undead and Dwarf units.
SOLID UNITS
A solid unit is defined as an Infantry unit with 20 or more troops, or a Cavalry Unit with 10 or more troops. For every solid unit, you can include 1 Hero/Monster unit and 1 War Engine unit. Note that the solid unit, Hero/Monster unit and/or War Engine unit must be from the same army list.
For example, a twenty-strong unit of Blacksouls would allow me to include the Abyssal Dwarf King and a Katsuchan Rocket Launcher in my army. It would not allow me to include an Orc Warlord and/or Undead Balefire Catapult.
A THOUGHT
So those restrictions are pretty straight forward - like the rest of The Kings of War ruleset. I read somewhere that it is designed to simple to learn, difficult to master - something that I definitely prefer to difficult to learn and difficult to master!
Looking at the army lists too (all of which are under two pages long), the units have very simple customisation options - which I think is great. I don't like to get bogged down with too many choices before even getting onto the table.
Sync out.