The History Channel: Crusades - Quest For Power, as the name implies, is a game about the wars between the Christian Crusaders and the so called "Infidels" for the Holy Land.
This is a RTS composed of 2 campaigns, each with 8 missions. You choose to play either as the Western Crusaders or the Eastern Infidels. Both armies have 4 unit types:
Infantry (west)/Warrior (east): costs 50 gold, average melee attack, poor defense (good against ranged), good movement;
Crusader (west)/Holy Warrior (east): costs 150 gold, good melee attack and defense, poor movement;
Archer (both): costs 100 gold, poor melee attack and defense, good ranged attack, average movement;
Priests (west)/Holy Man (east): no attack, poor defense, can heal other units.
You can create new units by building different tents for each of the three types of attack units, but you can't create new healing units. Creating tents and units will cost you gold, gathered from the corpses of dead enemies or found in treasure chests along the way.
As your units score kills against opposition units, they gain experience (measured by ranks out of 4). Higher ranks give the units special attack abilities (such as fire arrows). Throughout the missions you will also collect ancient relics which will upgrade your healing units (Priest/Holy Man) abilities. Units that survive a mission will proceed to the next one.
Besides the campaign mode, you can also play a random skirmish between the Western Crusaders and Eastern Infidels.