I'll start with the victory conditions. In order to understand the conditions, we need to know the backstory. The entire galaxy have been inhabited by the "Immortals". They are technologically advanced, so much that they've been looking for alternative types of entertainments. One proposed the idea of a gladiator-style arena in a cordoned off area of the galaxy. The players involved will use races that've been genetically created for the game. A player may decide to use a race that've been designed already, or to create his own. All races involved follow a set of rules, so no race is more advantaged or disadvantaged than others.
After all Immortals selects a race, the area is set up for the game, with special space monsters placed to guard valuable planets, and some technology artifacts to spice up the game. A system is set aside, called "Beyaan", that oversee the game and ensure that rules are followed. It is also guarded by the Immortals so the races can't invade it.
Now the victory conditions are the following:
Be the sole survivor - Wipe out all other races
Be the leader - You must be allied with races, and elected their leaders. All other races not allied with you must be wiped out
Kill the Immortals - Challenge the Immortals in Beyaan and crush them
Each of the victory will have a different ending. Sole survivor results in you winning the award. Leader results in the award being shared with other players. Killing Immortals results in your exile and you wipe out the immortals with the new superior race.
I've always disliked the diplomatic victory in MoO 1/2, I felt it was a bit too easy. Command a lot of planets so you can have a lot of votes for yourself, and bam! victory. In this, you are required to make and keep allies, and to convince them that you should be the leader. Not only that, all other races not allied must be either wiped out or form alliance with you.