The Great Divide (the Xi'an Civil War) took place from MXY 0.9311 - 0.9605 (20044 to 19770 BCE). The outcome of millennia of inter-House conflicts and complex webs of enmity and allyship, it began when the last daughter of House Kl.ō attempted defection to House Uai'i. Hostilities between the Houses grew deadly, and Houses Chii and Ru'a were compelled to join a now system-wide civil war.
The war concluded when members of House Kl.o sabotaged RyiXy'an's (Hyoton III) network of antique weather satellites, intending to assassinate the leadership of Houses Uai'i, Ru'a, and Chii during tentative peace talks. This inadvertently triggered a chain reaction that destroyed RyiXy'ans atmosphere, rendering the planet uninhabitable and killing millions. Survivors evacuated to the colony world Ka'ua (Hyoton IV).
The events of the Great Divide forced the Xi'an to reassess their culture. The calendar was reset to I.0 (19668 BCE), the Civil Service was established, a new capital was established on Ka'ua, and Ru'a was elected to serve as the first Imperial House.