The Twilight of a Northern Empire

In the fourth year of the Tianbao era (745 CE), the Later Turkic Khaganate – once the dominant power of the northern frontiers that had risen alongside the Wuchuan faction – finally collapsed, marking the end of an era. This event didn’t occur in isolation but represented the culmination of decades of decline for the Turkic empire and the calculated strategies of Emperor Xuanzong’s court.

The terminology change ordered by Emperor Xuanzong in 744 CE, replacing “year” (年) with “zai” (载) in official records, reflected his imperial aspirations to associate his reign with the legendary sage-kings Yao and Shun. This symbolic gesture coincided with the final dismantling of the Turkic threat that had loomed over China’s northern borders for generations.

The Long Decline of the Later Turks

The Later Turkic Khaganate’s fortunes had been waning since the early years of Xuanzong’s reign. The once-formidable Ashina Mojuo, who had previously challenged Empress Wu’s authority, found himself increasingly outmaneuvered after Xuanzong ascended the throne. Tribal confederations began defecting back to Tang allegiance as they recognized the new emperor’s firm stance.

The turning point came in 716 CE when Ashina Mojuo was killed during a campaign against the Nine Tribes of Tiele. This triggered a succession crisis that saw Ashina Mojuo’s sons murdered by Ashina Kutluk’s son, Ashina Qutlugh Tegin, who proclaimed himself as Bilge Khagan. The new ruler adopted a conciliatory approach, sending envoys to request vassal status (“to serve the Son of Heaven as a father”) in 721 CE and subsequently participating in Xuanzong’s Fengshan sacrifices.

Xuanzong’s Northern Strategy

Rather than pursuing traditional marriage alliances that might bolster Turkic prestige, Xuanzong implemented a more sophisticated strategy of economic warfare. The Tang established thriving border markets at Shuofang where silk and manufactured goods were exchanged for Turkic warhorses. This commercial engagement simultaneously enriched Tang coffers while making the nomads dependent on Chinese products.

When internal strife erupted in 734 CE with the poisoning of Bilge Khagan, Xuanzong saw an opportunity to restore Tang dominance reminiscent of Taizong’s era. He began actively interfering in Turkic politics, supporting rival factions, and preparing northern garrisons for action.

The Final Collapse

By 742 CE, the Tiele tribes – Uyghurs, Karluks, and Basmyls – exploited Turkic weakness to overthrow the ruling khagan. The Tang strategically supported these rebels, with Shuofang military commissioner Wang Zhongsi coordinating joint operations. In 744 CE, Uyghur leader Kutlug Bilge Kaghan defeated his former allies and established the Uyghur Khaganate, promptly seeking Tang recognition.

The coup de grâce came in January 745 when the Uyghurs executed the last Turkic khagan, sending his head to Chang’an. With Turkic remnants surrendering, the northern frontier entered a period of unprecedented peace. The Uyghurs expanded across the former Turkic territories, becoming the new steppe power while maintaining generally positive relations with Tang China.

Wang Zhongsi: The Guardian of the North

The stability owed much to Wang Zhongsi, the brilliant frontier commander who served as military governor of Shuofang and Hedong. Unlike aggressive border generals, Wang prioritized defense over offense, famously declaring: “In peaceful times, a general’s duty is to protect the people. I refuse to exhaust China’s strength chasing personal glory.” His network of fortresses stretching thousands of li created an impregnable northern barrier.

Wang’s background was particularly noteworthy – orphaned when his father died in battle against Tibet, he was raised in the palace alongside the future Emperor Suzong. This dual connection to both emperor and crown prince made him uniquely positioned to balance military effectiveness with political loyalty.

The Darkening Political Climate

While the north stabilized, ominous developments unfolded at court. Xuanzong’s infatuation with Yang Guifei (formerly his son’s wife) symbolized the emperor’s moral and political decline. The Yang family’s rapid accumulation of power and privilege, coupled with extravagant displays like the famous lychee courier system, marked a stark departure from Xuanzong’s earlier austerity.

Meanwhile, Chancellor Li Linfu perfected his system of political terror. His destruction of potential rivals – including the purge of the “Crown Prince faction” and the eventual downfall of Wang Zhongsi – demonstrated the toxic political environment. Li Linfu’s policy of promoting non-Han generals (like An Lushan) to prevent the traditional “general-to-chancellor” career path would have catastrophic consequences.

The Military Reorganization and Its Consequences

The Tang military structure underwent significant changes during this period. The consolidation of regional commands under single military governors created unprecedented concentrations of power. Figures like Wang Zhongsi briefly held four simultaneous governorships, while An Lushan would eventually command three. Li Linfu’s advocacy for “barbarian” generals – precisely because their illiteracy prevented them becoming chancellors – removed crucial checks on military authority.

This systemic weakness became apparent during the final years of Xuanzong’s reign. The emperor’s increasingly arbitrary decision-making, exemplified by the costly assault on Stone Fortress City (demanded against Wang Zhongsi’s advice), revealed a regime losing strategic coherence. The promotion of generals like Gao Xianzhi through court connections rather than merit further eroded military effectiveness.

The Gathering Storm

By 745 CE, the Tang empire appeared supremely powerful – the Turks vanquished, the Uyghurs cooperative, and military glory abundant. Yet beneath this golden surface, the rot was spreading: corrupt governance, factional strife, overextended frontiers, and an aging emperor distracted by personal pleasures. The An Lushan Rebellion (755-763) would soon expose these vulnerabilities, but its seeds were sown in the political and military developments of the Tianbao era.

The fall of the Later Turkic Khaganate thus marked not just the end of one nomadic empire, but the beginning of the end for Xuanzong’s golden age. The very strategies that brought victory in the north – reliance on non-Han generals, centralized military command, and court intrigue over sound governance – would soon turn against the Tang dynasty with devastating consequences.