This is a guide on basic and intermediate base defense building, originally written by Xwarrior411
Base defense is the measures you take to prevent the enemy from destroying your fort or even your home base. You have many buildings and techniques you can use to have the best fortification possible. You have Walls, Towers, Gates, and AA Towers (in WWI+) as your basic tools, and there are even more measures you can take, such as placing temples and universities everywhere in your base. You can also add capitols and have the range extend to everyone within and partly outside of your base for morale bonuses, and Cloaking if you have the power. You may also place walls and towers intelligently by placing them where they're not likely to get destroyed. Sealing your base from forests and mountains is a good idea because if your enemy has Pathfinding or makes units with that ability by default, and you rely on the mountain/forest to act as your wall, you're screwing yourself.
Walls are your main source of defense in Empire Earth, they seal off your base from enemy units and protect everything inside. Placing walls is easy to do but hard to do it intelligently. Doing it intelligently is ideal as it will make your walls harder to destroy, since it'll have fewer weaknesses. You should seal your base off from outside forests and mountains, as pathfinders can easily penetrate you if you don't. Another way is to place nearby Temples and Universities nearby to protect from that damned Prophet wiping your defenses out with an earthquake or firestorm, or priests weakening your internal defenses by converting your own troops to fight for THEM! At first a few units lost sounds like nothing, they're your own troops that are weakening you, every time you kill a converted unit, you've just killed a unit you've spawned. Building local towers to fire at attacking units is a must, which everyone will do, no matter the skill level. However, placing towers in wrong places can block the LOS of the tower, making it unable to fire at troops until the thing obscuring their view is destroyed (Usually the wall you wanted to protect in the first place)
Towers will fire on ground and sea units on sight, with the projectile fired from dependent on what age the walls and tower are. (Middle Aged towers fire arrows, while futuristic towers shoot lasers). Placing towers in good areas will not only make them more effective in killing off any attacks, they will be protected by the wall that it's defending. The Wall is the shield, the tower is the sword. You'll need a lot of 'swords' near your 'shields'. The more you have, the better.
Gates are actually converted walls to form a special wall that opens and closes to you and your allies, and stays closed to enemy troops. They consist of five tiles' worth of walls, and are actually slightly weaker then the five wall units added up. Also note that gates are often destroyed first as killing it is the same as taking down five walls, and it's large, allowing more melee units to attack it at once.
This is a must if your in an age that has airplanes/helicopters, you are able to build Anti-Air guns when airplanes come out, in WW1, you'll want a good number of them along with AA units to kill any planes that dare fly near your fortress.
This is a must for any long-term fortification. A temple is needed to protect you from the enemy's Prophets and his deadly disasters, you may need more then one if your base is large. Temples also let you make your own prophets and priests, which make great guardsmen to stay at home just in case you get attacked, they can greatly assist your defending army.
This may be optional depending on how your opponent(s) like to play. If you fear of your base falling from converted troops, you should invent in this building to ward the priests away.
Morale is a useful element of gameplay in EE, it protects units with damage reduction when within a capitol or town center's range with houses inside them, so it's advisable to make capitols/town centers that cover your whole base and place lots of houses, then all of your defending troops will take a lot less damage
A Defending Army
No matter how good your defensive structures are placed, it'll fall if you don't have help, usually a defending army which consists on units well suited in defending your base from attackers. You should have a good number of Archers/mortars/whatever unit can attack over walls...your walls, they'll be safe from the attackers (onless the attacker's using units that attack over walls, siege hurts...
Beware of siege weapons, they can destroy structures faster then normal units, so if you see them approaching, make killing them your first priority. Also watch out for bombers and the nuke, as this can kill all of your defenses you've worked so hard to set up in one run...
A good defense needs a good offense as well, the goal of Empire Earth is to kill the enemy's base. If all you do is build a base, the enemy will wipe your base out if you never even make an offensive strike on the enemy, suppressing the enemy can occur from attacking the enemy's base(s), as the enemy will likely use the troops he was gonna attack you with to protect his base(s), which gives you time to make yet more troops to attack the enemy.