(1) The Founding of Koryo and National Reunification

At the end of the 9th century, during the reign of Queen Chinsong, Shilla fell into a state of confusion with a weakening of royal authority. Rebellions sprung up everywhere and clan chiefs dominated the local areas. In the territory of Paekche, Kyonhwon established Later Paekche and in the territory of Koguryo, Kung'ye established Later Koguryo. In this way, Shilla was split into three territories which became known as the Later Three Kingdoms. Kung'ye, the King of Later Koguryo which was the greatest among the Later Three Kingdoms, was driven out by his subjects and then Wang Kon took the crown to found Koryo (918).
Wang Kon, later known as King T'aejo, renamed Later Koguryo as Koryo as an expression of its restoration and moved the capital from Ch'olwon to his hometown of Song'ak (Kaesong). This founding king aggressively won the powerful local chiefs over to his side, and adopted a policy of love for the people to win over the hearts of the people. Thus, the power of Koryo was strengthened.
King Kyongsun, the last sovereign of Shilla, followed the popular sentiments of the people and ceded his sovereignty to Koryo in 935. Thus Shilla fell. In the following year, Koryo attacked Later Paekche, which had been weakened as a result of disputes, and destroyed it in 936. With this, the Later Three Kingdoms, which were in a state of confusion for over 40 years, were reunified by Koryo.
Even before this, around the time of its downfall the majority of the Parhae ruling class surrendered to Koryo. Koryo received them and achieved national reunification.
In order to restore the old territiory of Koguryo, King T'aejo employed a policy to expand to the north. P'yong'yang was referred to as Sogyong (Western capital) in order to build it into an operational base to develop the north. In the last years of the reign of King T'aejo, the national territory expanded up to the Ch'ongch'on River and Yonghung.

(2) The Establishment of the Ruling Structure

In the early stage of Koryo, local chiefs held a great deal of power, and as a result of the King's political decision to enter into a marriage of convenience, members of the Queen's family entered the palace. The king's authority lacked stability. Thus, Koryo needed to firmly establish a central authority for political and social stability.
In order to establish his own authority, King Kwangjong suppressed the powers of the chiefs as well as the Queen's family. He enforced a law governing slaves and set free the slaves who were unlawfully owned by the chiefs. He enforced a Kwago, civil service examination system and employed officials based on the results of these examinations. As a result, the powers of the chiefs were weakened and royal powers were strengthened.
Under the reign of King Songjong, more refined institutions were adopted to maintain a system of centralized ruling power. He adopted the ideas of Ch'oe Sung-no, a Confucian scholar-statesman, to make Confucianism the political ideology and reformed the central government organizations and local administrative organizations. Such measures were almost completed during the reign of King Munjong.
As the central political organization, King Songjong set up the organizations of Naesa munhasong (later changed to Chungso munhasong), Sangsosong and Chungch'uwon (central council). The Chungso munhasong determined state policies. The Sangsosong was the executive branch and was composed of six departments-Personnel, Military, Treasury, Justice, Rites and Construction-which covered all the official administrative matters. The Chungch'uwon was in charge of receiving and promulgating the King's orders and military secrets. In addition, accounts were kept by the Osadae (office of the inspector) and Samsa, which was in charge of receiving, delivering, and keeping the accounts of money and grains.
In the Tobyongmasa (General Military Command), composed of high officials from the Chungso munhasong and Chungch'uwon, they decided on the important policies of the state. The Tobyongmasa was changed to Topyonguisasa in the latter period of Koryo and developed as the supreme organization of the state.
During early stage of Koryo, local administration was left to the autonomy of the chieftains, but under King Songjong, 12 divisions to which governors were dispatched were established. Later, local administrative organizations were gradually readjusted and divided the whole country into five provinces and two special provinces. In the two special provinces, military commanders were dispatched and in the five provinces, provincial governors were stationed to govern the cities, counties and Hyon. Hyang, So and Pugok were created, which were special administrative districts where the menials lived.
As military organizations, "Two Armies" and "Six Guards" were established as central structures and local armies were also set up. The Two Armies served as the King's royal guards, and the Six Guards were charged with policing the central city (Kaesong) and responsible for national defense. The Supreme Commander of the Two Armies and Six Guards was the Sangjanggun (High general). A military council (Chungbang) gathered to consult on military affairs.
The system of land distribution was overseen by the Chonsikwa which was first organized during the reign of King Kyongjong, and then reformed under King Mokjong on the basis of official status. In Chonsikwa, officials were divided into 18 classes and given farms and forestland according to the ranks of the officials. When the officials died, the land was, in principle, returned to the state. Pieces of land referred to as Kongsin-jon were given to meriting vassals, Kong'um-jon were given to officials above the 5th rank, and Naejang-jon were given to members of the Royal House. These lands could be handed down to one's descendants.

(3) Centered on Family Lineage

During the Koryo dynasty, family lineage was regarded as very important. Men born to well-off families enjoyed many privileges as aristocrats. They occupied high government positions and possessed large acreages of farmland. The male children of officials above the 5th rank became government officials without having to pass the civil service exams. This was referred to as the Umso system and aristocrats from good families could retain a high government office for many continuous years.
During the middle period of the Koryo dynasty, powerful families controlled the government. They married into the royal house and became powerful members of the Queen's family. Examples of such aristocratic families were the Yi clan of Inchu, the Kim clan of Kyongju and the Ch'oe clan of Haeju.

The Koryo society consist of 4 classes. The high class consisted of the royal family and high aristocrats, the middle class consisted of lower level bureaucrats and technical bureaucrats, the lower class commoners, and the lowest class consisted of menials and slaves. Thus, the middle classes composed of the lowest group of rulers, commoners, and menials were the governed.
Merchants and handicraft workers were members of the commoner class. They were responsible for production and bound to provide taxes, imposts and corvee. Slaves, butchers, actors and residents of Hyang, So and Pugok were considered menials.
In Koryo, the government organizations of Uich'ang (righteous warehouse), Sangp'yongch'ang (ordinary warehouse) and Bo (foundations) stabilized the life of farmers. To provide relief to poor peasants, the Uich'ang stored and loaned grains during famines or in the spring. The Sangp'yongch'ang purchased grains when prices were low, and when prices soared, it sold the grains in order to regulate the prices. So, Chewibo was a kind of foundation which existed in order to relieve the poor. In addition, the Tong-taebiwon and So-taebiwon (emergency centers of the East and West) were medical facilities for the poor.
Industry was centered on agriculture, but the commerce and handicraft industries developed gradually. With the rise in commercial activities, pieces of iron "Konwon-chungbo", "Samhan-t'ongbo" and "Tongguk-t'ongbo" as well as silver bottles were used as currency. But these currencies were not widely circulated.
In the Koryo dynasty, "Yondunghoe" and "P'algwanhoe" were observed to offer sacrifices to the indigenous gods. The people engaged in playing ball, riding swings and wrestling during the "Tano" festival which always fell on the fifth day of the fifth month of the lunar calender.

(4) The Military Regime and Changes in the Ruling Power

Entering the 12th century, the foundations of the family-centered aristocratic society began to shake. A member of the Queen's family, Yi Cha-gyom declared war in 1126, and Myoch'ong began a movement to relocate the King's court to Sogyong (P'yong'yang) in 1135. These incidents were pacified, but the abuses and contradictions within the aristocratic society were not rectified. To compound the situation, the practice of favoring civilians and discriminating against the military within aristocratic society became more acute.
The military, who were long discontent over their discrimination, rose up with disgruntled others with Chong Chung-bu as their leader in 1170. They deposed and exiled King Uijong, and killed many civilians in order to set up a military government.
The new ruling power of the military continued to engage in in-fighting over who would retain power, and this further aggravated political and social confusion. By the end of the 12th century, Ch'oe Ch'ung-hon retained dictatorial power and settled the confusion to some degree.
The military coup d'etat shook the family-centered aristocratic society of Koryo. It brought down the civilian structure of control and the military occupied all of the high and important positions. Corruption and tyranny ran rampant under their rule and caused great suffering among farmers and menials. As a result, the peasants everywhere rose up in rebellion, shaking the very foundation of society.
Under the guidance of Mang'i and Mangsoi, peasants and menials rose up and in Myonghak-so, Kongju and in Chonju, government slaves rebelled. In Kyongsang-do peasant rebellions under the leadership of Kim Sa-mi and Hyo Sim broke out, and in Kaegyong, Ch'oe Ch'ung-hon's slave Manchok planned a movement to emancipate slaves.

(5) Struggles Against the Northern Tribes

In the Koryo dynasty, the northern tribes of Qidan, N zhen, Mongols were very strong, but by waging fierce struggles against them Koryo safeguarded the country and its people.
Koryo implemented a policy of expanding northward from the beginning of its national foundation. Qidan, which stood in confrontation with Song, felt uneasy with Koryo's pro-Song and northward expansion policies and frequently tried to invade Koryo. Under the reign of King Songjong, Koryo's So Hui had a bout with the invading Qidan commander, and retrieved six towns south of the Yalu River. During the reign of King Hyonjong, the Koryo army under the command of Kang Kam-ch'an nearly destroyed the Qidan army which invaded Koryo in Kwiju for the third time. This is known as the Victory of Kwiju (1019) In the 12th century, the N zhen tribe expanded their power to cover the northeastern frontier territory of Koryo. A special unit led by Yun Kwan conquered and built nine walls around the area because of the repeated appeals by the N zhen tribe when this territory was returned.
Afterwards, the N zhen, which had regained much strength, founded the nation of Jin and became a powerful nation dominating northern China. Koryo received pressure from Jin for a time, and to repel this, the monk Myoch'ong proposed relocating the capital to Sogyong and sending an expedition against Jin.
Ch'oe Ch'ung-hon's dictatorial regime was succeeded by his descendants for four generations during 60 years while the Ch'oe clan strengthened their military government. The Mongols became a powerful world empire in the Asian continent during the 13th century. By demanding that Koryo pay unreasonable tributes the Mongols oppressed Koryo during the reign of King Kojong. The Mongols launched a full-fledged invasion of Koryo in 1231. Military dictator Ch'oe U moved the King's court to Kanghwa Island and prepared to engage in battle. The Mongols invaded Koryo many times for 40 years, but Koryo resisted with the solidarity of the whole nation. The valiant struggles of the peasants and menials were particularly worth noting.
But a coup took place in Kanghwa. Ch'oe's military regime crumbled and an approchement appeared between Koryo and the Mongols. Finally, peace was negotiated and the King's court returned to Kaegyong. However, the military unit, the Sambyolch'o, under the command of Pae Chung-son opposed the return of the capital to Kaegyong and continued the war against the Mongols. They moved their base of operations to Chindo and Chejudo, where they continued the resistance struggle for four years. They were finally suppressed by the allied forces of Koryo and the Mongols in 1273.

(6) Safeguarding Independence

After the end of the resistance of Sambyolch'o, Koryo was invaded and pressured by the Yuan (the Mongols named their dynasty Yuan) and Koryo independence was challenged. As a result of pressure by Yuan, Koryo was forced to provide ships and military forces to two expeditions to Japan by the Yuan. Yuan established the Ssangsongch'ong branch of government to govern the land north of Ch'ollyong. With the intervention of Yuan, the official organizations of Koryo were restructured.
But even under the intervention of Yuan, Koryo maintained national sovereignty and made efforts to drive out the forces of Yuan. In the mid-14th century, when Yuan was driven back northward by the newly rising kingdom of Ming, King Kongmin adopted an anti-Yuan policy of self rule and enforced reform in politics.
King Kongmin attacked the government branch, Ssangsong, and recovered the land north of Ch'ollyong. He restored the official organizations of the nation, expelled pro-Yuan officials and prohibited the practice of Yuan customs. At the time, powerful aristocrats occupied large tracts of land and owned many slaves. The King returned these unlawfully occupied lands to their rightful owners and liberated the slaves. Due to opposition by powerful aristocrats, the King's reform measures failed.
Japanese pirates and the Chinese Red Turbans invaded frequently, bringing heavy losses to the Koryo people. In the process of repelling these invasions, military power increased. Ch'oe Yong and Yi Song-gye became famous generals. At the end of the 14th century, an expedition to conquer Liaodong was discussed among the circles of Ch'oe Yong, but on his march north, Yi Song-gye, who led this expedition, went as far as Wihwa Island on the Yalu only to do an about-face. In Kaegyong, he took power and made preparations to establish a new dynasty with a group of new scholars.