The Interstellar War is referred to as such, not because it was the first such occurrence, but because it had such drastic effects upon the galaxy that no one has bothered to talk about any other war since.
Culminated by Human ambition, the Interstellar War was fueled by the constant threat of the Phage. The humans advertised their control of the deadly organism in order to sway the rest of the galaxy under their control. Although only officially declaring war against one faction (backed by the Alkor race in the Hizara system), the human empire essentially took control of the entire galaxy through military means. Once the rest of the interstellar civilizations had agreed to a human controlled “Alliance”, the Imperialists turned their eyes upon the defiant Order of the Fist in 15537 C.E.Y. The Order refused to become a puppet to the Imperialist government, and so fought bitterly to protect their space from the rest of the known galaxy.
Although vastly outnumbered, the fiercely militant Order managed to prevent the Imperial Alliance Fleet from ever reaching the gates of the Hizara system, and eventually pushed them back into the Ek system. The humans learned that the Order of the Fist had successfully created a ship-mounted planet-destroying weapon, and fearing an inevitable push by the technologically superior Alkor, the humans used their agents in Hizara to plant the Phage weapon throughout the system in 15604 C.E.Y. The Phage eradicated almost all life in the system, leaving only the Order’s vast fleet.
Preparing for the inevitable backlash, the Imperial Alliance Fleet (IAF) pushed into the Dead system, then stood their ground. It was here where that the Last Battle was fought, and 98% of the IAF was destroyed, along with most of the Order’s ships (and accordingly, most of the Alkari race). Believing that a great goal had been achieved by halting the deployment of the planet-destroyer, the Imperialists declared victory for themselves after the Last Battle.
However, the massive assault by the Order was only a distraction by the Alkari. The true goal was to slip a small group of ships past the defensive line into Allied space. These ships carried recovered samples of the Imperialists Phage weapon, and proceeded to drop the organism into every habitat in the galaxy. The resulting wave of destruction is estimated to have eliminated 99.9% of known life in the galaxy. The ultimate goal was the destruction of the Imperialists and the Sol system. However, this was prevented by the Preservationists by closing off all of the hyperspace entrances into Sol in 15606 C.E.Y.