The human diaspora from Terra in the Galactic South began with the discovery of jump technology in Ancient ruins among the moons of Jupiter.
A period of colonialism followed; the powers of Earth spread their tendrils through the South, and escapists fled further afield. The galactic North was colonized by religious zealots, the West by libertarians, and East by philosophers. Ancient ruins were found throughout the galaxy; some were lived in or explored, but most were ignored.
The South remained the cultural and political center of human life. Great Merchant Houses evolved from the corporations of the 20th century. The Confederation of Free Worlds developed in the West for mutual protection against the encroaching Terran Hegemony. The Shaper culture evolved in the East in pursuit of transcendence. The North remained fractured between competing religious sects until sudden unification under the First Prophet, Nehemiah Scudder.
Scudder established the Ordos Templari and launched the Great Crusade to take back Earth and unite mankind under the Divine Imperium. The Crusade proceeded successfully until Scudder was slain during the Siege of Terra. Terra fell, but the Crusade stalled.
A decade later, the Imperium is still trying to unite all of mankind under a single banner. The Confederation of Free Worlds is coming apart around the edges, with Imperial influence strong along the border, and the Shapers are gradually dying out as they trade lives and planets with the Templars. For their part, Scudder’s successors have divided the Imperium into fiefdoms whose lords answer only to the highest heads of the Church.