Conflict

Koguryo continued its expansion through the Korean peninsula, using its elite military class, the "kyon-dang." Its expansion reached a peak, in the fifth century AD, when it had gained control of half of the Korean peninsula and much of Manchuria. With the start of invasions by Koguryo and the hostile Han (Chinese) tribes from the north, and Paekche's growth from the west, Silla was compelled to defend itself.

In 540 AD, after King Chin Hung had assumed power in Silla, came many years of wars between Silla and Koguryo. However, before Koguryo was engaged, King Chin Hung took on the task of driving the Japanese colonies in the south out of Silla. At about this same time, a small Kaya league had formed in the area between Paekche and Silla that had strong ties with the Wa State of Japan. King Chin Hung annexed the portion of the Kaya league that was in alliance with the Yamato Clan of Japan.

King Chin Hung then turned his armies toward the fertile valleys in central Korea, between the Han and Imjin Rivers. The conquest of Han-Imjin River area brought great wealth to Silla through the acquisition of the richest agricultural lands in the peninsula and of its peasantry labor. This conquest also opened an easier route to China through the capture of ports on the Yellow Sea. The acquisition of iron mining regions led to new technological gains that predicated even greater expansion by Silla.

King Chin Hung asked the famous Buddhist priest, Wan Kwang Bopsa, to develop a system of martial arts that was in harmony with his concepts of the laws of nature. The result was the creation of the Hwarang warriors who played a crucial role Silla's efforts to unify Korea. The Hwarang are discussed in detail in a later section of this topic.

From 632 to 654 AD, two queens inherited the Silla throne in their own right, indicating a significant difference between ancient Silla practices and the male-dominated hierarchy of China. Silla's 27th ruler, Queen Son-dok, (reigned 632-647 AD) quickly established good relations with T'ang China, and introduced many Chinese customs, such as fashions in court dress. She also sponsored and supported the Hwarang-do and sent many Hwarang warriors on expeditions into China to learn Chinese war tactics. Her nephew, who later became King Mu-yol , the 29th ruler (reigned 654-661 AD), and his son, King Mun-mu, the 30th ruler (reigned 661-681 AD) led Silla in its efforts to unify the Korean peninsula.

As a part of its unity efforts, Silla sought the aid of the T'ang Dynasty in China. The Silla envoy to the T'ang court, Kim Chunch Ue, attained an alliance with the Chinese military to fight against Koguryo and Paekche. The agreement said that, if the united forces defeated Koguryo, the land south of P'yongyang would belong to Silla and China would get all land to its north, and, if they defeated Paekche, the entire country would belong to Silla.

The T'ang attacked Paekche from the sea, and Silla forces, led by General Kim Yu-sin (a Hwarang), attacked from the land. In 660 AD, the alliance defeated Paekche. However, the T'ang government ignored its agreement, established five military bases in Paekche, and attempted to establish pro-Chinese enclaves inside Silla. Although this angered Silla, since it was still battling Koguryo, it did not have the resources to resist the T'ang.

In 661 AD, a northern invasion into Koguryo by the T'ang and a southern invasion by Silla were not successful, but they did weaken Koguryo defenses.

During this critical time, the king of Koguryo, Yon Kae So Mum, died. leaving his brother and two sons battling for power. Due to Koguryo's internal strife, the continuous battles, and a Koguryo defector named Namsaeng, Koguryo was finally defeated in 668 AD, by the T'ang (under the leadership of Li Chi, invading from the north) and Silla (led by Kim In Mum) attacking from the south.