The Clone Doctrine was introduced during the reign of the Taiidani Emperors, instated when Emperor Riesstiu IV murdered all of his relatives out of fear of assasination. The doctrine states that the current emperor's genetic template be recorded, so when he dies, a clone will be grown to take his place, instead of placing somebody else on the throne. The result (after Riesstiu IV's death) was Riesstiu IV the Second.
Because of this decree, the Imperial Gene Banks were a major target of the Taiidan Resistance after the Emperor's death at the hands of the Kushan. By destroying the banks, the Rebels ensured that there be no new emperor, causing internal struggles in its remnants.