In 327AE Lukaz found that large sections of the Federal Imperium were corrupt, so he took the hard stance against it that many wanted and, in a contraversial move, dismissed the entire Imperium. Soon after he was assassinated.
The vaccuum in power left caused the outbreak of hostilities, as the military tried to take over for the good of everyone and the "disposed" Federal Imperators objecting and trying to reclaim their lost power.
Fighting started almost immediately, and dozens of factions appeared, all vying for control of key planets and systems, jokeying for position with quickly patched together fleets and support. By ealry 328AE the Federation was a "no fly zone" and solid information on what was happening nside its boarders was hard to come by.