The Fractured Empire: China After the Fall of the Sui

When Li Yuan (later Emperor Gaozu of Tang) seized the Guanzhong region in 617 CE, China lay fractured into competing power blocs following the collapse of the Sui Dynasty. The Eastern Capital Luoyang remained the ultimate prize, controlled first by the rebel leader Li Mi, then by the warlord Wang Shichong who defeated him. Meanwhile, Dou Jiande dominated the fertile Hebei plains. These three figures—Wang, Dou, and the defeated Li Mi—represented the major obstacles to Tang unification.

Beyond these primary rivals, smaller but strategically positioned warlords controlled critical territories. In the northwest, Xue Ju and his son Xue Rengao held Tianshui and the Longshan passes. The self-styled “King of Liang” Li Gui dominated the Hexi Corridor, while Liu Wuzhou, allied with the Eastern Turks, controlled Shanxi’s northern frontier. These regional powers, though individually weaker than the Tang, occupied formidable terrain that could threaten Li Yuan’s rear during eastern campaigns.

The First Challenge: Xue Ju’s Northwestern Offensive

The initial threat emerged from Xue Ju in southern Gansu. In 617, as Li Yuan consolidated Guanzhong, Xue forces advanced along two invasion routes toward Chang’an:

1. The Southern Route: Through the Long Mountains to Fengxiang (ancient Fufeng), controlling the upper Wei River valley
2. The Northern Route: Via Liupan Mountains to Jingchuan, exploiting the Pingliang corridor

After Xue Rengao’s defeat at Fengxiang, his father switched strategies. In 618, Xue Ju bypassed Tang defenses at Jingzhou, creating the war’s most critical moment. Historians note that had Xue not died unexpectedly during this campaign, the Tang might have lost their capital before establishing stable governance.

Xue Rengao’s subsequent surrender and Li Gui’s defeat in the Hexi Corridor by 619 secured the Tang’s western flank, allowing preparation for the eastern campaign against Wang Shichong’s self-proclaimed Zheng regime in Luoyang.

The Northern Crisis: Liu Wuzhou’s Shanxi Campaign

Just as the Tang prepared to march east, Liu Wuzhou—former Sui officer turned Turk-allied warlord—launched an audacious southern offensive from his base in Mayi (modern Shuozhou). His strategy mirrored Li Yuan’s own path to power:

1. Phase One: Bypass Taiyuan (held by Li Yuanji) to capture Yuci and Jiezhou
2. Phase Two: Establish strongholds like the fortified village of Zhangbi with its multi-level tunnel networks
3. Phase Three: Control the Longmen crossing to threaten Guanzhong from the northeast

By 619, Liu controlled nearly all Shanxi except the Henei region. His general Song Jinggang besieged Tang forces at the strategic village of Baibi—a loess plateau fortress controlling access to three critical routes:

– West to the Yellow River crossings
– Southeast to Luoyang via Yuanqu
– North along the Fen River to Taiyuan

Li Shimin’s Masterstroke: The Baibi Campaign

The future Emperor Taizong implemented a multi-phase counterstrategy:

1. Logistical Preparation: Stockpiled grain in Baibi’s elevated position
2. Attrition Warfare: Avoided direct combat while raiding enemy supply lines
3. Strategic Pursuit: Crushed Song’s retreating army after six months of starvation tactics

Liu’s collapse was spectacular—abandoning all gains from Taiyuan back to Mayi before fleeing to the Turks. This victory eliminated the last major threat to Tang’s heartland, demonstrating three key military principles:

1. Terrain Utilization: Loess plateau fortresses as force multipliers
2. Economic Warfare: Targeting supply lines over battlefield confrontation
3. Psychological Impact: Rapid collapse of overextended armies

The Road to Unification: Strategic Implications

With Shanxi secured by 620, the Tang held overwhelming geographic advantages against Wang and Dou:

– Western Strongholds: Controlled all passes into Guanzhong
– Northern Buffer: Neutralized Turkic allies through Liu’s defeat
– Economic Base: Secure access to Shanxi’s iron and horse resources

The campaigns against regional warlords established critical patterns for Tang military success: combining fortress warfare with mobile cavalry tactics, leveraging Turkic alliances while preventing their expansion, and systematically eliminating peripheral threats before engaging central rivals. These lessons would prove decisive in the coming showdowns at Luoyang and Hulao Pass.

Legacy: How the Early Campaigns Shaped Imperial China

The 617-620 campaigns established enduring templates in Chinese military history:

1. Strategic Sequencing: “Secure the periphery, then conquer the core” became standard doctrine
2. Loess Warfare: Plateau fortification systems influenced frontier defense for centuries
3. Turkic Relations: Demonstrated both the necessity and danger of steppe alliances

Modern archaeological sites like Zhangbi’s tunnels and Baibi’s earthworks preserve tangible evidence of this pivotal transition from Sui collapse to Tang order—a testament to how calculated regional campaigns enabled China’s next golden age.