The Rise of Tibet and the Fragile Balance of Power

The unraveling of the Tang Dynasty’s “Tiankehan” (Heavenly Khan) tributary system—a network of alliances that secured China’s dominance over Central Asia—began with an unlikely disruptor: Tibet. In 650 CE, the death of Tibetan King Songtsen Gampo marked a turning point. His young successor, Mangsong Mangtsen, inherited the throne under the regency of the formidable chancellor Gar Tongtsen Yülsung (Lu Dongzan in Chinese records).

Tibet’s emergence as a regional power defied geographical logic. The harsh Tibetan Plateau, with its sparse arable valleys, seemed an improbable cradle for empire. Yet under Songtsen Gampo, Tibet had leveraged climate warming and strategic marriages—including the famed 641 CE union with Tang Princess Wencheng—to jumpstart its civilization. Gar Tongtsen, the architect of Tibet’s expansion, had witnessed Tang grandeur firsthand as the envoy who negotiated the princess’s marriage. Emperor Taizong had even attempted to recruit him as a Tang agent by offering an aristocratic bride—an offer Gar Tongtsen deftly declined.

The Battle for the Silk Road

Gar Tongtsen recognized that Tibet’s survival depended on accessing the wealth of the Silk Road. In 659 CE, a decade after Taizong’s death, Tibet launched a devastating war against the Tuyuhun Kingdom—Tang’s key ally controlling the Southern Silk Road (Qinghai Corridor). By 663, Tibetan forces under Gar Tongtsen’s son Gar Trinring Tsendro (Qinling) expelled Tuyuhun ruler Murong Nuohebo from the plateau.

This conquest gave Tibet control over critical trade routes. As the Old Book of Tang notes: “Though illiterate, [Gar Tongtsen] possessed brilliant military judgment. Under him, Tibet became a formidable power.” The Qinghai Corridor wasn’t just economically vital—it gave Tibet the strategic high ground to threaten China’s Northern Silk Road.

Tang’s Fatal Missteps

Emperor Gaozong and Empress Wu Zetian disastrously underestimated the threat. In 665, they prioritized a lavish Mount Tai封禅 ceremony over military response. The extravagance bankrupted the treasury, forcing a currency debasement (“Qianfeng Quanbao” coins worth ten times face value) that triggered economic collapse.

Tibet exploited Tang weakness. In 670, Gar Trinring captured the Four Garrisons of Anxi—Kuqa, Kashgar, Khotan, and Karashahr—severing Tang’s western lifeline. A Tang counterattack led by general Xue Rengui ended catastrophically at the Battle of Dafeichuan (670), where Tibetan forces annihilated Tang armies and dashed hopes of restoring Tuyuhun.

The Domino Effect: Collapse on All Fronts

Tibet’s victories exposed Tang vulnerabilities. In 678, another 180,000-strong Tang army was crushed near Qinghai Lake. By 679, as Tibet consolidated power under the young king Tridu Songtsen, rebellions erupted across the frontier:

– Western Front: Tibet repeatedly severed the Silk Road until 692, when general Wang Xiaojie temporarily reclaimed the Four Garrisons.
– Northern Frontier: The Eastern Turkic Khaganate rebelled in 679, capitalizing on Tang’s distraction. A disastrous 681 massacre of surrendered Turks by Chancellor Pei Yan destroyed Tang’s credibility, fueling the rise of Ilterish Qaghan’s Second Turkic Khaganate.
– Northeast: In 696, Khitan chieftains Li Jinzhong and Sun Wanrong revolted after Tang officials extorted their tribes. The 13-month rebellion—only suppressed with Turkic “help”—left lasting scars.

Wu Zetian’s Diplomatic Disasters

Empress Wu’s policies accelerated the collapse:
– The Currency Crisis: The 666封禅 debacle and coinage reform crippled Tang finances.
– Strategic Blunders: Abandoning the Four Garrisons in 686 invited Tibetan reconquest.
– Catastrophic Alliances: Her 698 deal with Turkic ruler Qapaghan Qaghan—trading surrendered tribes for military aid—violated Taizong’s principle of protecting vassals. The Turks later pillaged northern China with impunity.

The Legacy of Failure

By Emperor Xuanzong’s reign (712–756), the damage was irreversible:
– Tibet dominated the Southern Silk Road
– The Second Turkic Khaganate raided at will
– Khitan and奚 tribes remained hostile

The once-mighty Tiankehan system lay in ruins. Xuanzong’s creation of military节度使 (jiedushi) governors—a desperate measure to secure the frontiers—would later enable the An Lushan Rebellion (755), dooming the Tang’s golden age.

The lesson was clear: when empires prioritize pageantry over strategy and betray their allies, even the “Roof of the World” can become their undoing. Tibet’s rise proved that in the high-stakes game of Eurasian power, geography is no barrier to ambition—only to recovery.