1 . Dong Zhou's Assassination
After 18 months in retirement, Cao Cao returned to the capital Luoyang in 188. That year, he was appointed Colonel Who Arranges the Army (典軍校尉), fourth of eight heads of a newly established imperial army, theArmy of the Western Garden. The effectiveness of this new force never became known, since it was disbanded the next year.
In 189, Emperor Ling died and was succeeded by his eldest son (Emperor Shao), although state power was mainly in the hands of Empress Dowager He and others. The empress dowager's brother, General-in-Chief He Jin, plotted with Yuan Shao to eliminate the Ten Attendants (a group of influential eunuchs in the imperial court). He Jin summoned Dong Zhuo, a seasoned general of Liang Province, to lead his army into Luoyang to pressure the empress dowager to surrender power, despite accusations of Dong's "infamy". Before Dong Zhuo arrived, He Jin was assassinated by the eunuchs and Luoyang was thrown into chaos as Yuan Shao's supporters fought the eunuchs. Dong Zhuo's army easily rid the palace grounds of opposition. After he deposed Emperor Shao, Dong Zhuo placed the puppet Emperor Xian on the throne, as he deemed that Emperor Xian was more capable than the original puppet Emperor Shao.
After rejecting Dong Zhuo's appointment, Cao Cao left Luoyang for Chenliu (southeast of present-day Kaifeng, Henan, Cao's hometown), where he built his army. The next year, regional warlords formed a military allianceunder Yuan Shao against Dong. Cao Cao joined them, becoming one of the few actively fighting members of the coalition. The coalition fell apart after months of inactivity, and China fell into civil war while Dong Zhuo was killed in 192 by Lü Bu.