The Goguryeo-Sui Wars
But the Sui Emperor was not done yet. Amazingly despite the massive defeat suffered the previous year, and the rising turmoil, Emperor Yang declared a new campaign for Goguryeo shortly after New Year’s, 613. This time around more care was taken in regards to supplies and logistics, with the Sui Army establishing supply bases along the Liao River and to Wanghaidun, a Sui controlled port in Manchuria. The Emperor also gave a great degree of latitude and free reign to his generals, realizing by now just how much he hampered the war in 612. Once again all troops were ordered to converge on Zhuo Commandery.
Cavalry battle between Goguryeo and Sui
The fubing and professional forces arrived as they did the previous year, but the conscripts arrived in reduced numbers. Many of the conscripted soldiers deserted from their formations rather then go to war, inflaming an already bad situation in the countryside, where banditry was rampant. In response, and perhaps because he was disappointed in the performance of his professional troops, Emperor Yang ordered the formation of a new army for this renewed invasion. This new army was called the Xiaoguo Army, or the Army of the Brave and Determined. The xiaoguo troops were, unlike the fubing or the conscripts, a voluntary formation. Mostly made up of local strongmen and their followers, the xiaoguo formations were a throwback to Western Wei’s local elite forces. They were also totally devoted to Emperor Yang, who rewarded that devotion by attaching the Xiaoguo Army to the command structure of his personal bodyguard.
{default}The sources are not clear when the second expeditionary force began to move but by the end of March the army had reached the Liao River. On the other side of the line in Goguryeo the royal court in Pyongyang could hardly believe the Sui would launch another invasion so soon. Eulji Mundeok, the hero who saved Goguryeo in the first invasion, was already dead, killed during the Sui pullout. Nevertheless King Yeongyang was optimistic. Even without Eulji his strategy could still work, the defensive plan could still hold. On May 21st the Sui expedition crossed the Liao River into Goguryeo. Emperor Yang divided his force into three: the main column under the Emperor’s personal command would besiege Ryotongsong. A second column would besiege Sinsong (known to the Sui as Xin). A third column, organized into a strike force, was dispatched to capture Pyongyang. The naval forces of Lai Hu’er, still at dock in Shandong, were ordered to work in close tandem with the strike force this time. The main focus of this invasion was on the siege of Ryotongsong. Despite the great skills of the Chinese siege engineers, employing every engine they could construct, the fortress held out. On July 20th dire news arrived for Emperor Yang. Back in China Yang Xuangan, no relation to the imperial family, had launched a revolt. Yang was the ambitious son of Yang Su, a trusted advisor and Prime Minister for Emperor Wen. But under Emperor Yang the fortunes of the family took an abrupt turn.
The new Emperor neither trusted nor liked Yang Su or his family, despite their vital contribution to his taking the throne. Yang Xuangan grew despise the Emperor after he overheard him say that if Yang Su hadn’t died when he did the entire family would have been executed. After that Yang began to plot against the Emperor. After being entrusted with overseeing the supplies at Liyang he saw his chance. On June 25 Yang Xuangan declared rebellion at Liyang, stating that Emperor Yang was unfit to rule. The rebels’ official aim was to depose the ruling emperor and restore the empire to the balance and prosperity it enjoyed in Emperor Wen’s reign. When news reached the imperial camp at Ryotongsong it threw the entire expedition into a uproar. Emperor Yang immediately called off the invasion and ordered the entire force to turn around and march back to China. Lai Hu’er, who had just set sail for Pyongyang, was ordered to use his naval forces to impede the rebel advance on Luoyang. Little did the retreating Sui forces know how close they were to succeeding in their aim.
When news of the rebellion reached the Emperor the fortress of Ryotongsong was ready to fall. The Goguryeo forces, unsure of whether or not this was all an elaborate ploy, did not pursue at first. But a combination of the defection of General Husi Zheng and the speed with which the Sui were retreating, convinced them it was real. The Goguryeo gave chase, ransacking the abandoned camps for weapons and gold and at the Liao River they fell on the Sui rear guard, killing thousands. The rebellion was put down in two months, but the affect it had on the weakening Sui state was dire. Yang Xuangan had not acted alone, and his rebellion represented the turning of the tide against the Sui. The influential military houses, whose support had been crucial in Emperor Wen’s reign, had begun to resent the increasingly tyrannical nature of Emperor Yang’s rule. This, coupled with a new round of rebellions all over the empire, was effectively the beginning of the end.
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Also it should be noted that while Chinese fortifications during this era were built from bricks baked out of mud, Goguryeo fortifications made from stones which were denser and harder material. Therefore Chinese siege equipments which were designed to besiege Chinese fortresses were ineffective in sieging Goguryeo.
Also Goguryeo used scorched earth tactics extensively against Sui. During retreat Goguryeo army burned all grains, buried alive all livestocks, and even poisoned the water supplies in order to prevent them being captured by the opponent.
This was particularly the reason why the 300,000 men Sui strike force was doomed, as they were unable to resupply themselves locally.
Unlike modern era, ancient warfare consistently faced challenges in supplies in logistics, and often times the armies relied on the supplies captured locally. Even Sun Tzu in his art of war stated that supplies captured from the enemy was worth 20 times that of one’s own supplies. This was a sound assessment, due to the combined factors of gaining the supply + reducing the supply needs required in order to supply one’s army + reducing the supply of the enemy.
Goguryeo’s scorched earth tactics were particularly effective against large armies such as Sui, as larger armies are often more vulnerable to supply shortages. This is the reason why later Tang Taizong opted to field smaller forces of elite units in frequent raids rather than fielding gigantic armies like Sui had. As effective a tactic scorched earth is, the toll is also significant to the defenders as well. Decades of war against Tang in this scenario eventually ended with succumbing of Goguryeo.