The Hidden Cracks Beneath the Golden Age: Military Decadence in Kaiyuan’s Northeast Frontier

The Glorious Facade of Kaiyuan’s Golden Age

The Kaiyuan era (713-741) under Emperor Xuanzong of Tang stands as one of China’s most celebrated golden ages. Poet Du Fu’s nostalgic verses paint an idyllic picture: “In the complete prosperity of Kaiyuan days/Small towns held ten thousand households’ stays.” Granaries overflowed with grain, merchants traveled safely without fear of bandits, and the empire enjoyed unprecedented cultural and economic prosperity. This was an era when “the roads across the nine provinces knew no tigers or wolves,” and the empire’s prestige stretched across the continent.

Yet this glittering surface concealed troubling developments along the volatile northeastern frontier, where military governors (jiedushi) operated with increasing autonomy. The same frontier that protected the heartland from Khitan and Xi tribes would eventually birth the catastrophic An Lushan Rebellion in 755. How did this military decay take root during China’s supposed golden age? The answer lies in the forgotten campaigns against the Khitan chieftain Ketugan and the disturbing patterns established by successive frontier commanders.

The Rise of a Khitan Nemesis: Ketugan’s Challenge

The Khitan tribes of Manchuria had long been a thorn in the Tang empire’s side. In 696 during Empress Wu Zetian’s reign, Khitan leaders Li Jinzhong and Sun Wanrong rebelled, annihilating a 280,000-strong Tang army in one of the dynasty’s most humiliating defeats. Though temporarily subdued, the Khitan threat resurged under the brilliant but ruthless chieftain Ketugan during Kaiyuan.

As deputy commander of the Jingxi Army, Ketugan first demonstrated his political cunning in 720 by overthrowing his superior Li Suogu. When the Tang-backed Li Suogu fled to Yingzhou seeking help, Ketugan defeated the relief force, killing both Li Suogu and the Xi chieftain Li Dabu who had supported the Tang. Yet in a masterstroke of political theater, Ketugan immediately petitioned Emperor Xuanzong for forgiveness, maintaining plausible deniability while consolidating power.

For over a decade, Ketugan became the de facto ruler behind a series of puppet Khitan leaders, playing the Tang against the Eastern Turks. His true ambitions became clear in 730 when he murdered the last figurehead leader Shao Gu and defected to the Turks with both Khitan and Xi tribes in tow. This brazen act forced Emperor Xuanzong to authorize a massive punitive expedition under Prince Li Hui, involving troops recruited from across northern China.

Military Mismanagement on the Frontier

The Tang response to Ketugan’s rebellion revealed systemic problems in frontier military administration. Zhao Hanzhang, the military governor of Youzhou (modern Beijing), led the vanguard force in 732 with characteristic recklessness. Ignoring warnings from his subordinate Wu Chengci about possible ambushes, Zhao pursued retreating Khitan forces straight into a trap at Mount Baobai.

Only Wu Chengci’s last-minute flanking attack saved the Tang army from complete destruction. When the main force under Prince Li Hui arrived, they routed Ketugan’s forces, but the Khitan leader escaped to fight another day. Zhao Hanzhang’s subsequent punishment—execution for embezzlement—highlighted the corruption festering among frontier commanders.

Zhao’s successor Xue Chuyu fared no better. In 733, he dispatched general Guo Yingjie with 10,000 cavalry and 25,000 Xi auxiliaries to finish Ketugan. At Mount Dushan, they encountered Ketugan’s combined Khitan-Turkic force of 100,000. The Xi troops deserted en masse, Guo Yingjie died heroically leading a charge, and 6,000 Tang soldiers fought to the last man rather than surrender. Yet Xue Chuyu had his secretary Fan Heng draft a victory report (lubu) claiming glorious triumph, a deception that earned him only dismissal when the truth emerged.

Zhang Shougui: The General Who Could Have Changed History

The Tang finally found an effective commander in Zhang Shougui, appointed in 733. A veteran of campaigns against the Tibetans, Zhang combined military brilliance with psychological insight. Rather than costly frontal assaults, he employed subterfuge, sending his aide Wang Hui to negotiate with Ketugan while secretly contacting the disgruntled Khitan general Li Guozhe.

In 734, Li Guozhe assassinated Ketugan and surrendered to the Tang. Zhang’s bloodless victory marked the pinnacle of his career—he was feted in Luoyang, awarded honors, and celebrated in verse. Yet his ambition to become chancellor was blocked by chief minister Zhang Jiuling, who distrusted military men. This rejection set in motion Zhang’s tragic decline.

Desperate for further glory, Zhang began falsifying reports of minor victories. In 737, after his subordinates provoked an unnecessary battle that ended in defeat, Zhang covered it up by bribing the investigating eunuch Niu Xiantong. When the scandal broke, Niu was executed gruesomely, while Zhang was merely demoted to a provincial post where he died soon after, his reputation in tatters.

The Fatal Legacy: An Lushan’s Rise

Zhang Shougui’s most fateful act was sparing a young officer named An Lushan. Caught stealing sheep in 732, the multilingual Sogdian-Turkic officer talked his way out of execution by appealing to Zhang’s ambition. Zhang made An his adoptive son and protege, promoting him despite a disastrous 737 defeat that should have meant execution. Even when chief minister Zhang Jiuring warned that An had “the face of a rebel,” Emperor Xuanzong pardoned him.

After Zhang Shougui’s fall, An Lushan cultivated connections at court, rising to command three frontier districts. His practice of provoking then crushing Khitan and Xi tribes created a self-sustaining cycle of rebellion and promotion. By 755, he controlled nearly 200,000 troops—the largest force under any Tang general—which he turned against the dynasty, unleashing the devastating An Lushan Rebellion.

Conclusion: The Systemic Roots of Collapse

The northeastern frontier’s decay during Kaiyuan’s golden age reveals fundamental flaws in the Tang military system. Frontier commanders, distant from central oversight, developed dangerous autonomy. The pursuit of merit-based promotions encouraged reckless aggression and falsified victories. Most crucially, the Tang failed to integrate successful military leaders like Zhang Shougui into central governance, leaving them to pursue ever-greater conquests.

As historian Sima Guang noted in the Zizhi Tongjian, “The seeds of the An Lushan rebellion were sown in the Kaiyuan era.” The glittering prosperity of Xuanzong’s reign concealed structural weaknesses that would nearly destroy the Tang dynasty. This cautionary tale reminds us that even golden ages contain the seeds of their own undoing when military power becomes detached from civilian oversight and accountability.