From the late 230s, tensions began to become visible between the imperial Cao clan and the Sima clan. Following the death of Cao Zhen, factionalism was evident between Cao Shuang and the Grand Tutor Sima Yi. In deliberations, Cao Shuang placed his own supporters in important posts and excluded Sima Yi, whom he regarded as a dangerous threat. The power of the Sima clan, one of the great landowning families of the Han dynasty, was bolstered by Sima Yi's military victories. Additionally, Sima Yi was an extremely capable strategist and politician. In 238 he crushed the rebellion of Gongsun Yuan's self-proclaimed Yan Kingdom and brought the Liaodong region directly under central control. Ultimately, he outmanoeuvred Cao Shuang in power play. Taking advantage of an excursion by the imperial clansmen to the Gaoping Tombs, Sima Yi undertook a putsch in Luoyang, forcing Cao Shuang's faction from authority. Many protested against the overwhelming power of the Sima family; notable among these were the Seven Sages of the Bamboo Grove. One of the sages, Xi Kang, was executed as part of the purges after Cao Shuang's downfall.