Zone of Control
Also referred to as the defense area and taking "free shots" or "potshots"
The Zone of Control is what a very select group of units have that allows them to attack any units when they move into a square within one square of the unit without getting attacked back. The units that have this are AEGIS Cruisers, Armies, Cavalry, Chinese Riders, German Panzers, Horsemen, Iroquois Mounted Warriors, Marines, Mech Infantry, Modern Armor, Paratroops, Radar Artillery, Russian Cossacks, and Tanks. This is how it works. Example: Look at your keyboard, off to the right is the number pad. Pretend that these keys are squares in the game and any one of these "Zone of Control" units is on the number 5 key. Now pretend that an enemy warrior with 4 Hit Points walks into square 6. Your unit will do nothing if he does decide to attack you. However, if he chooses to pass into square 8, your unit will shoot him, he will now have 3 hit points, and there's nothing he can do about it. If he's really stupid and decides to walk into square 4, your unit takes another shot, and he's down to 2 Hit points. When he leaves, simply finish the job next turn. That's it. I know because I've seen it happen. ANY UNIT CAN GAIN A ZONE OF CONTROL BY BUILDING A FORTRESS AND PLACING THE UNIT INSIDE.