Yuan Zhen suppressed Zhang Hu due to political rivalry and Zhang Hu's perceived threat to Yuan Zhen's power. Yuan Zhen, a prominent figure in the Tang Dynasty, was the son of Emperor Gaozong and Empress Wu Zetian. He ascended the throne in 712 and faced numerous challenges, including the influence of his mother, Empress Wu, and the growing power of Zhang Hu, a military general and statesman. Zhang Hu's rise to prominence was rapid, and he held significant power over the military and government. However, Yuan Zhen viewed Zhang Hu as a potential rival and a threat to his authority. To consolidate his power, Yuan Zhen resorted to suppression, which included political intrigue, accusations of treason, and ultimately, the execution of Zhang Hu.

The suppression of Zhang Hu was driven by several factors. Firstly, Yuan Zhen was concerned about the concentration of power in Zhang Hu's hands. Zhang Hu's military successes and political influence had made him a formidable figure, and Yuan Zhen feared that he could challenge his authority. According to the "Tangshu," a historical text, Zhang Hu was accused of having ambitions to become the next emperor, which further fueled Yuan Zhen's suspicions.

Secondly, Yuan Zhen was influenced by his mother, Empress Wu, who had a history of using political intrigue to consolidate her power. Empress Wu's influence on her son was significant, and she may have advised him to suppress Zhang Hu to maintain stability in the empire.

Data from the "Tangshu" and other historical sources indicate that Yuan Zhen's suppression of Zhang Hu was not an isolated incident. During his reign, Yuan Zhen faced numerous challenges from powerful officials and military leaders who threatened his authority. For example, he executed his own brother, Li Longji, in 710, in a bid to eliminate potential rivals. The suppression of Zhang Hu was part of a broader strategy to maintain control over the empire and ensure his own survival as the ruler.

In conclusion, Yuan Zhen suppressed Zhang Hu due to political rivalry and the perceived threat to his authority. The concentration of power in Zhang Hu's hands, combined with the influence of Empress Wu, led Yuan Zhen to take drastic measures to eliminate a potential rival. The suppression of Zhang Hu was a critical event in the Tang Dynasty, highlighting the political intrigue and power struggles that characterized the era.