By taking control of one of the sixteen species in Orion in an attempt to claim dominance..or defeat in the Orion Sector.
It turns out that what was thought to be Antares in Master of Orion II was really "ConJenn," a forward base for the Antarans. After faking their eradication for 25 Galactic Cycles, the Antarans returned to defeat the young races of the Orion Sector over the course of another 25 G.C. They enslaved whole planets, destroyed all technologies and military outposts and effectively made it impossible for a retaliation of any kind.
At the beginning of MOO3, set a thousand years later, the Antarans have mysteriously disappeared. The disappearance coincides, it is discovered, with the release of a prototype virus-like organism, Harvester Gamma. Harvester Gamma would infect and multiply, potentially destroying any species it was set loose on. In an ironic turn of events, the organism was accidentally loosed on the Antarans, wiping out 98% of their population in the Antaran sector.
The survivors on Orion declare themselves the "New Orions" (not to be confused for the "Ancient Orions"). The remaining Antarans, in a remote outpost, begin work on another Biological weapon, called Harvester Zeta while the "New Orions" grant the rebellious colonies in the Orion sector a new Orion Senate, and pretend to play the role of benevolent, and enlightened leadership. The Antarans unleash the Harvester Zeta on a remote Human settlement, but Harvester Zeta, a sentient organism, begins to call itself the Ithkul and form its own colonies like the other races in the Orion Sector.Gameplay
Changes Since MOO2
The gameplay in Master of Orion 3 was somewhat changed from Master of Orion I and II. This had to do with the change of development staff, and the implementation of new features. The new features of 3 were derived from a fan-service vote, whereby the features of the game would be dropped or minimized or maximized according to what gamers wanted. The essential change in MOO3 from MOO2 is that micromanagement (a noticeable complaint from gamers) was toned down significantly, and although things were streamlined on paper, the game never lived up to its promises, and many of the game's fan-voted-ideas never saw the light of day (such as colonization of moons and asteroids, and a racial ethos system). However, many of the more irritating mechanics from MOO2 were revamped for the better, such as the race customization feature and the fleet system. New to the series was ground combat, which allowed units to wage war in a "paper scissors rock" sort of way (although it never really worked out the way intended). The developers added a real-time battle system that, for good or ill, was indeed real-time. Victory Conditions
Upon choosing your species and race, you undertake the conquest of the Orion Sector through either diplomacy, military conquest, or technology.
- Leadership of the Galaxy (winning election to the Galactic Senate) - in order to do this you were required to get the other races in the galaxy to vote for you, which may or may not require military force, but always required cold, hard diplomacy. It was the easiest of the three victories in MOO3.
- Military Conquest (Destruction of all other races) - As is quota for all 4X games, Military Conquest is the most difficult of all the victory conditions in MOO3, partially due to the game's extremely aggressive AI, but also due to the fact that sieging a planet can take over a hundred turns, and causing genocide en masse, and destroying all civilizations can take long over 1000 turns.
- Finding the Antarian X's - As a departure from the series, instead of just conquering the Antarian homeworld (though you can conquer the Orions, and a good luck to you if you try), you can find the Antarian X's, which reveal more of the Antarian's backstory. Doing this requires the sending out of high-priced exploration fleets.