Command and Conquer [1995; Westwood Studios]
Spawning seven sequels, the original Command and Conquer pitted the Global Defense Initiative against the Brotherhood of Nod, a terrorist cult intent on control of valuable tiberium crystals, with the player controlling whichever side they'd like. One of the games that popularized the genre, it also featured live-action cut-scenes.
Starcraft [1998; Blizzard Entertainment]
The best-selling videogame of 1998, Starcraft put the player in the midst of a heated war between the Terrans, Protoss and Zerg for control of the galaxy. Players had to capture resources, train and develop an army and fight off their opponents. Starcraft also had an addictive multi-player mode, allowing complete strangers to team up against the computer.
Warhammer 40,000: Dawn of War [2004; Relic Entertainment]
An adaptation of the tabletop game, Dawn of War featured space marines fighting for interstellar dominance. Building upon elements of previous real-time strategy games, Dawn of War added close combat units, grouped squadrons and troop morale to the proceedings. Also, you could zoom in and watch your genetically engineered robo-soldiers get all stabby on space monsters. Yeah.