An artifact is uncovered by a jedi excavation team, and it appears to be a part of a star map. More peices start appearing in other factions coi, and as more of the map is unveiled, it becomes more and more obvious that once all the parts are aligned the map will function once again. Some factions band together to try and complete most of it, but alas it takes cooperation from every factions leaders to align the final pieces.
Having seen the map, and recorded its information, the sith and Jedi present do what they do best, while other members of the factions flee with their version of the information.
The factions all arrive on world, only to discover that it's nothing special on the surface, and has no real interesting facets, other than native humanoids. So naturally the factions gear up, and roll out the war machines.
However the factions soon discover, after a skirmish or two, that there's a network of caves they can take advantage of to strike at their enemies. However, the caves run deeper than they predicted, and they accidentally awaken some form of uncontrolable horde of foul creatures, which proceed to try and ravage the planet and kill everything there (think necrons from 40k). It becomes apparent that these creatures could eventually pilot or create ships, for they already have primitive blaster technology from pre-clonewars, indicating theyve been sealed down there for thousands of years.
Rather than glassing the planet, which wouldn't reach then depths of the caves, the factions (while still warring with eachother, AND the admin run beasties) opt to send teams down into the caves to try and massacre the creatures at their source.
They come across a few nests, maybe find some hoarded thigs from ancient times, and eventually by chance find a monolithic structure in a cave larger than any they've seen before. Natrally this is where the creatures progenitor is, and part of it is visible from outside the monolith, so they opt to band together and try to kill it while it's here.
They battle their way up the structure while the battle above gets more and more intense, until they eventually kill the creature. Then the beasties all turn tail and flee. However it turns out the beasts vague movements and ability to dtand on its own legs was keeping a part of the structure up.
The monolith begins to collapse, and the cave roof thatnit was supporting crumbles too, which causes a chain reaction, and a few hundred mile wide crater rapidly begins to form.... right under the area that the people on the surface are fighting on.
Fight turns to flight, and everyone tries to make it to safety - this leads to people being mixed in with other factions, and trapped behind enemy lines or outright captured.
End event. Hand out suitable prizes.
Begin rp to free/take back hostages.