The Goguryeo-Sui Wars
The invasion had now begun. By choosing to get under way just after the New Year’s ceremony Emperor Yang made clear that he intended to blitz through Manchuria as fast as possible. Ahead of the rainy season that had caused his younger brother’s expedition so much trouble. His aim was to capture Pyongyang and force King Yeongyang to submit, not to conquer Goguryeo. At Shandong the new fleet set sail under the command of Lai Hu’er, Senior General of the Left Wing Guard, and the Sui Navy soon established dominance over the waves. In Goguryeo the defensive preparations were being completed and made ready for war. The long wait between King Yeongyang’s defiance and the actual setting out of the expedition had given Goguryeo much needed time to prepare the defenses for the coming onslaught.
{default}As the Sui Army advanced the Goguryeo forces in Yingzhou, still there from the war in 598, fell back as the terrain would not work to their advantage this time. Eventually King Yeongyang himself ordered them to abandon the area and retreat behind the Liao River. The defense plan that had been put together by Goguryeo was entering the final stages. The plan was primarily focused on bogging down the Chinese forces in lengthy sieges. Much of Manchuria was dotted by fortresses, the most formidable being the moon shaped river fortresses. These fortresses were all well fortified and defended by locally recruited forces and kyongdang youth bands. Since the Sui could not afford to advance with these hostile strongholds in the rear they would have to besiege them. If the Sui did manage to advance onwards then they would have to deal with the roving tangs (bands of warriors rallied around a local lord called a tangju), the provincial armies, and lastly the royal army. On April 19th, 612 the Sui Army finally arrived at the Liao River. However they were not alone as a force of Goguryeo soldiers had drawn up on the other side. Three pontoon bridges were then designed by the chief engineer of the expedition, Yuwen Kai (a relative of Yuwen Shu, who was the Emperor’s star general), and deployed across the river. Under withering fire from the enemy on the eastern bank the Sui discovered the pontoons were too short. A fierce melee resulted as Emperor Yang ordered his army to try to cross the river anyway. They were repulsed by the defenders and forced back to the western bank.
Several days later new pontoons were constructed and laid across the Liao. This time around the pontoons stretched all the way to the eastern bank, allowing the Sui Army to cross. A second melee followed and this time they were victorious. Emperor Yang ordered his forces to press on. The Goguryeo forces fell back and reorganized themselves near the Ryotongsong fortress. There they were defeated in open battle by the Sui, who moved on to besiege the fortress itself. Ryotongsong, which was called Liaodong by the Chinese, was the key to the entire valley, and had to captured. But much to Emperor Yang’s dismay it would prove to be a tough nut to crack. Because of the fortifications of the walls, and the spirit of the defenders (led by the naval hero Gang Yi-sik).
Now the most grueling part of the campaign began. Not long after the siege of Ryotongsong began the Sui became aware of the other fortresses that were also heavily garrisoned. The initial strategy had involved being able to reach Korea proper before the Goguryeo forces could disperse into the fortresses. But each fortress always had a permanent garrison and the Sui were faced with a bad situation. Deciding that his siege train would be enough to level the Manchurian fortresses Emperor Yang opted to reduce the enemy strongholds first, then move on. However at the same time the Emperor effectively crippled his own efforts.
Before the army had set out from Zhuo Commandery Emperor Yang had given orders that his generals were not to act independently, but check back with him before giving their orders. On the other side of the line King Yeongyang left his generals to their own devices, trusting them to wage the war on his behalf. Goguryeo soon discovered this fatal flaw in the command structure of the Sui when, as Yodong fortress surrendered, rather then accept it the Senior General instead sent a messenger to the Imperial Camp. The commanding songiu (literally: castle lord) of Yodong took advantage of the lull to reinforce his position and rest his troops. When the affirmative arrived from the Emperor the offer was no longer good and the siege resumed. Exploiting this loophole the various songiu would pretend to surrender, and take the time it took for the messages to go back and forth to reinforce and rest. Using this system the fortress line in Manchuria held out, and by June no progress had been made. By now Emperor Yang had become aware of what was going on, and he knew a change of strategy was needed. The rainy season would soon begin, and if he could not make any gains by the time the rain fell then the entire enterprise would have come to nothing. With this in mind the Emperor put into motion a bold new strategy.
The decisive campaign had begun. Realizing that a new strategy was needed if he was going to salvage a victory from this war Emperor Yang decided to detach nine armies, or 300,000 men from the main body of the expedition. This force would be refitted for a quick decisive campaign, a surgical strike to capture Pyongyang. So that the strike force could proceed with out hindrance each soldier was issued enough grain for 100 days. Ironically this extra ration, which normally would have been received with cheers, only increased the heavy burden on the men. Despite this Emperor Yang threatened beheading to any man found throwing his grain away. However the soldiers still found a way to dispose the extra rations, by burying it during the night.
To command the strike force Emperor Yang choose his favorite generals, Yuwen Shu and Yu Zhongwen. Yu was appointed Senior General and Yuwen Deputy General. Realizing his past mistake the Emperor gave wide latitude to Yuwen and Yu, allowing them to do as they pleased on the field. In cooperation with the strike force the marines under General Lai were ordered to assist in the taking of Pyongyang. By mid July the naval forces of Lai Hu’er had already reached the Taedong River (where he was to meet the strike force), and had taken position a scant 20 miles from Pyongyang. By that time his forces had already engaged the Goguryeo, who had fallen back to the city as a ploy. General Lai soon grew impatient waiting for his land based allies to arrive and he proposed to his staff a new plan. General Lai would take 40,000 of his best marines and take Pyongyang before Yuwen Shu and Yu Zhongwen arrived.
Despite the pleas of his subordinates to wait for the main force Lai proceeded as he had planned and left the safety of his ships. This was exactly what the Goguryeo generals were hoping for and they ordered their men to fall back once again, which only inflamed the ego of General Lai even more. As the Sui marines entered the outer citadel the defenders scattered, with a picked force going into the shelter of a Buddhist temple. When Lai Hu’er allowed his men to break ranks and loot the picked force burst from cover and attacked. The Chinese were caught completely off guard, and as more and more defenders pored in Lai Hu’er ordered a retreat. By the time they reached the safety of the Sui Navy the once mighty marines had been reduced to a mere couple thousand men.
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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.