The Case of Duke Huan of Qi Detaining the Marquis of Cai

In 656 BC, Duke Huan of Qi, the hegemon, led an allied force to attack the State of Cai. The conflict stemmed from a personal dispute: Marquis Mu of Cai had remarried his daughter (Duke Huan’s former concubine) to another state after she annoyed Duke Huan during a boating trip. Enraged, Duke Huan invaded Cai, swiftly defeating it, and captured Marquis Mu. This action was subsequently framed as punishment for Cai’s disobedience to the Zhou royal authority. The detention was eventually resolved through diplomatic mediation by other feudal lords, leading to the marquis’s release.

Marquis Mu of Cai was defeated in battle, captured, and detained by Duke Huan of Qi. He was later released after other feudal lords mediated the dispute. The military action against the State of Cai was successfully completed.

Whether Duke Huan of Qi’s invasion and detention of Marquis Mu constituted a legitimate exercise of hegemonic authority to uphold feudal order, or an abuse of power driven by personal vengeance under the guise of a punitive expedition.

The case reinforced Duke Huan of Qi’s supremacy and his doctrine of "Revere the King, Expel the Barbarians," demonstrating that personal grudges between feudal lords could trigger large-scale military conflicts under the pretext of upholding the Zhou feudal order. It also highlighted the absolute power of the hegemon in arbitrating international disputes during the Spring and Autumn period, influencing the diplomatic norms of the era.