Empires & Allies handles combat in its own dedicated mini game of sorts. Whether you engage an enemy in the campaign or a friend by invading their empire, combat is handled in sort of a split screen representation of the units you sent into battle vs the units you either chose to attack or, in the case of the single-player campaign, the AI opponent randomly chooses. Battles, which are fully animated and turn based, are decided based on how each unit performs against another in what essentially amounts to a more sophisticated game of Rock, Paper, Scissors.
Empires & Allies isn't far different from CityVille in how it handles city building. So much so that cities exist almost separately from combat, only coming into play during combat when an empire is invaded. Players must build residences to increase their population, which dictates what military buildings they can create and thus military units. You also must create resource generating buildings like Farms, Lumber Mills, Oil Refineries and Ore Mines to provide you with resources necessary to create the advanced military units, which are placed around your structures to defend them from invasion. There are five types of Ore, and each empire only yields one type, which spurs trade amongst players for the Ores they can't access.
Empires & Allie's Neighbor Invasions is the crux of PvP in the game. Once you reach Level 6, you have the option to either invade a friend's empire or help it. Invading it allows you to choose and area that will yield the most resources, and attack it using your units compared to whatever defenses the opponent has in place. If you defeat the enemy, you will automatically collect resources from that invaded spot every few hours, or until the player or their friends kick you out. Invading more players increase your Infamy and unlocks special abilities you can use in combat. Of course, this all happen asynchronously.
Unfortunately, there isn't much to be said at the moment of Army Attack in the PvP department. You can't invade your friends' HQ nor can you engage them in combat, but you can always help them out with nifty air strikes against their AI enemy. Perhaps PvP will be added to the game later on, but at the moment it's nowhere to be found.
Both E&A and Army Attack offer deep strategic combat and interesting takes on conquering territories or establishing empires. However, the crux of any combat strategy game--even on Facebook--is player vs player battles. And seeing how Army Attack has yet to include the feature (though, it does allow players to help one another), we declare Empires & Allies the winner of this first Facebook Game Face-off. And now is the moment you've all been waiting for: It's time for you to decide the victor.