Warfare between Koguryo and China
Koguryo had been a longtime enemy of China during the time of the Han dynasty and continued to be an enemy of some of the smaller Chinese states after the fall of Han.
When the state of Sui unified China, it reflexively looked to Koguryo as a serious threat to its northern bor-der. Sui mounted a campaign against Koguryo. When this failed, Sui tried again and then a third time.
One of the greatest heroes in Korean military history was the gen-eral Ulchi Mundok (fl. early seventh century), who defended Koguryo against the Sui. Most of the fighting took place on the Liaodong Peninsula in Manchuria, not on the Korean Peninsula.
In one of the battles with the Sui dynasty, however, the Chinese forces spilled into the Korean Peninsula and closed in on the capital, Pyongyang. General Ulchi Mundok devised a plan whereby the Korean soldiers would feign defeat.
The Chinese, thinking a rout was on, pursued the Koguryo soldiers. Soon they came to a river, then called the Sal, now called the Taedong (Gabriel 1994).There, the Korean forces waited for the Chinese army to spread itself out as it crossed the river.
At the moment when the Chinese were not expecting it, the Koreans attacked and slaughtered thousands of the enemy. One account says the Chinese started with 300,000 men in their army and returned with only 2,700.
Little else is recorded about him, but Ulchi Mundok is remembered as a great hero. Although his family name was not passed down to the present day (unlike that of the Kims and others from Silla), still he is remembered.
One of the major streets in downtown Seoul bears his name, Ulchi-ro. After the Sui founder died, the state was unable to maintain its dynasty. Sui’s repeated attempts to conquer the Koguryo, which caused the deaths of thousands of Chinese soldiers and the bankruptcy of the royal treasury, led to its downfall.
The Sui dynasty was followed by the Tang dynasty (618–907), and they, too, tried repeatedly to conquer Koguryo. However, Koguryo proved remarkably resilient. It withstood six invasions from two of the most powerful dynasties China would ever know.
In the meantime, the southern part of the Korean Peninsula was locked in hostilities. Paekche attacked Silla, and Silla turned to Koguryo for an alliance to beat back the invasion. The competing three kingdoms had endured from the third to the seventh centuries through a balance of power. Like an equilateral triangle, a strong geometric structure, the three-sided political configuration remained well balanced.
Whenever one side seemed strong enough to take advantage of a weaker side, the weaker side would form an alliance with the third side, and the result was a stalemate and a continuation of the Three Kingdoms. By the mid-seventh century, however, these dynamics began to change because China had been reunified. Koguryo, preoccupied with invasions from China, turned down Silla’s request for an alliance after 642.