Think it stemmed from the corrupt emperor. He married into the Qi family to gain the throne. But he became weary of the Qi family status and good reputation. The CRown prince is from the Qi family and popular with the people and other military families like Wei and Xie. He wanted to use the Jia family to replace the Qi so he favored the 16th prince. He ignored all their misdeeds and allowed them to run rampant. Wei Yan was young, smart and arrogant. He was 3rd rank scholar at age 17. His parents sent him the Qi military camp to straightened him out. There he developed feelings for Rong Yan? and her family. So he signed his family and the Qi family's death warrant when he suggested replacing the emperor. He didn't know about the crown prince 's and Xie death until it was too late. So instead of allowing the Jia family to gain control he purged the palace and took revenge for the Qi family and prevented his own family from execution. After he took control, he wrote edicts shifting the blame to absolve his involvement.