The Great Fleet Massacre was the start of the Phoenix Dominion War. In July of 600 AW the Gren of the soon to be announced Phoenix Dominion stationed at key points in the navy murdered their fellow officers and attempted to take control of the twenty-one fleets of the GFAW Navy. Several fleets were aware of this happening and took measures to counter act this take over.
Still millions were killed and even more were killed as other Gren struck at several large star ports and drydocks. After the dust settled only seven fleets remained, though several were diminished below their original numbers.