"Star Wars: Empire at War is a 2006 real-time strategy (RTS) game developed by Petroglyph Games and published by LucasArts. Set between Episode III and Episode IV, it focuses on the fledgling struggle between the Empire and the Rebels. It uses Petroglyph's game engine Alamo. The most recent patch was released on July 20, 2006. In October 2006, an expansion entitled Star Wars: Empire at War: Forces of Corruption was released.
There are three game modes: storyline-based Campaign, Galactic Conquest and Skirmish. Battles can take place on a planet (land battle) or above the planet (space battle). Land battles are fought with infantry and ground vehicle units, while space battles are fought with starfighter squadrons and large spacecraft.
Galactic Conquest is the sandbox campaign, in which the player controls Rebel Alliance as it struggles to achieve freedom or command the Empire and strive to achieve galactic domination. A weaker, neutral faction of Pirates exists, but makes no attempt to battle the Rebels or Empire unless attacked. Each faction has at least one of three broad objectives for Galactic Conquest, which vary depending on which scenario is being played: kill the enemy leader (Mon Mothma or Emperor Palpatine), protect or destroy the Death Star, or completely remove the other faction from the campaign map. Grand strategy, production, and resource management is facilitated through a two-dimensional galactic map. The player receives funds from planets they control,and from mining facilities. Money is used to research technology, build defenses and vehicles, and train troops. Each planet confers different advantages to its owner, even though some bonuses are specific to each faction (for example, controlling Kuat reduces the price of Imperial Star Destroyers by 25 percent).
When enemy forces meet (either fleets in space or ground forces landing an enemy planet) a battle ensues. The player(s) can use only the equipment they brought to the battle (be it an X-wing squadron or an AT-AT). Factions must battle across both space and land maps. The defender may also use any buildings (land) or his space station (space) if he has constructed them. In each battle, each side may only have a certain number of units on the field at a time; the rest are retained as Reinforcements, which can be called in any time to designated areas when allowed. In land battles, a player can field more units at a time if he captures Reinforcement Points.
The storyline Campaign follows a semi-open linear path, where the given side must complete sequential mission objectives (such as stealing X-wing prototypes). Campaign missions build up to the plot of Star Wars Episode IV: A New Hope and eventually, the Battle of Yavin. Campaign is very similar to Galactic Conquest, although the Galactic Map is gradually opened for play as the player completes scripted events and completes missions.
Skirmish mode is the familiar, classic RTS mode. Skirmishes come in two types: land and space. In land skirmishes, all players start with bases and must research upgrades and capture resource nodes while fighting to destroy the enemy's base or command center. In space skirmish mode, all players have a space station that can be upgraded. The player buys land or space units to attack the enemy with until the enemy base/space station is destroyed or the enemy forces are destroyed. The player can advance in technology levels to access more powerful ships as the player gains more money. The player can build more buildings and defenses, and the space station can also be upgraded to better defend itself without requiring the player to leave ships behind to defend it. Skirmish battles require the least time investment, so it is better suited toward casual players. It also has some "free-play" to it. Maps can support two, three, or four players, and the difficulty is scalable as easy, medium or hard.
All modes are played in real time. Days on the galactic map pass continually. When a battle occurs, galactic time is paused while the battle wages. After the battle, the galactic day timer resumes. When playing against the computer, the player can accelerate time or pause time on both the galactic and skirmish maps.
All modes also make use of important Star Wars characters, such as Darth Vader, as Heroes. Each Hero is a single, moderately powerful unit with special abilities. For example, Obi-Wan Kenobi, Emperor Palpatine, and Darth Vader can use The Force. Some characters can be used in both land and space battles,(e.g. Darth Vader becomes a special tie fighter unit in space.) while others can be used only on land or only in space (a land-only Hero will remain on board a landing craft during space battles and have no use of their special abilities)."
Source: Wikipedia, "Empire_at_war," available under the CC-BY-SA License.