Dominance of the Imperium

Terran Expansion
The Terrans expanded for roughly four centuries, as far as their technology would allow them. On the way, they colonised vast swathes of the galaxy, and also encountered the first non-Terran races, which they forcibly subjugated to Terran rule. However, they expanded too far for their own good. Their empire became too large to manage effectively, and realisation that the Terrans were diminished in effective power led to a number of systems seeking independence. Some wished to be free from the harsh yoke that held them, others merely wished a modicum of independent power.

As the Terran Empire fragmented, many of the subjugated races decided to rise up against them. What began at first as an irritation soon turned to full scale war, as systems were captured and recaptured by both sides. Even those races fighting side by side against the Terrans often turned on one another, and Chaos consumed the galaxy.