The Annual Peace Feast is a celebration for the end of hostilities between Saturn's moon Titan and Mars. Only Men and Women who were deeply involved in the war (Admiral Bitchface, President Keith Caylo, Titan force five, The Martian priminister and the Hammerschmiddtt family are the only known attendees).
In the episode "Megamum Overdrive" it is stated that Mars is banned from making superweapons which would make you think that Titan won the war but the peace feast implys that the war ended in a Truce; The true outcome of the war may be revealed later on in the series. Or perhaps Titan won and this feast just signified the end of the conflict.
Just because Titan and Mars are not at war at the moment does'nt mean they have to like each other because as shown at the peace feast they will turn on each other in an instant. When Gibbs stole a cubic tonne of Martian fuel, Titan blamed Mars because their nukes were not competently protected but Mars blamed Titan because Gibbs is their rogue agent.
The Second and possibly Third Peace Feast was interupted by a terrorist attack orchestrated by the criminal mastermind Gibbs. A giant crab monster sent and controlled by Gibbs had abducted the convention center and attempted to throw it into one of the volcanoes of the planet Io; he was stopped by Troy Hammerschmiddtt who killed the crab monster by drilling through it with the bottom of the convention center. Unfortunately the Martian priminister had given up the trigger codes for the Atomic fuel before they were rescued.