Achievements

Starting politics based on Confucianism

King Sejong revolutionized government by appointing people from different social classes as civil servants. Furthermore, he performed official government events according to Confucianism, and he encouraged people to behave according to Confucianism. As a result, Confucianism became the social norm. He also published some books about Confucianism.

At first, he suppressed Buddhism by banning all Buddhist monks from Seoul, drastically reducing the power and wealth of the Buddhist hierarchy, but later he alleviated his action by building temples and accepting Buddhism by making a test to become a monk (Seung-gwa).

Foreign policy

In relationship with the Chinese Ming, he made some successful agreements that benefited Korea. In relationship with Jurchen people, he installed 10 military posts - 4 counties (郡) and 6 garrisons (鎭) - in the northern part of the Korean Peninsula.

He maintained good relations with Japan by opening three ports and allowing trade with them. But he also invaded Tsushima island with military forces in order to stop pirating in the South Sea (East China Sea) since Tsushima island was a base for pirates.

Strengthening of the Korean military

King Sejong was an effective military planner. He created various military regulations to strengthen the safety of his kingdom, supported the advancement of Korean military technology, including cannon development. Different kinds of mortars and fire arrows were tested as well as the use of gunpowder.

In May 1419, King Sejong, under the advice and guidance of his father Taejong, embarked upon the Gihae Eastern Expedition, the ultimate goal of this military expedition to remove the nuisance of Japanese pirates who had been operating out of Tsushima Island. During the expedition, 245 Japanese were killed, and another 110 were captured in combat, while 180 Korean soldiers were killed. 146 Chinese and 8 Korean kidnapped were liberated by this expedition. In September 1419 a truce was made and the Korean army returned to Korea, but the Treaty of Gyehae was signed in 1443, in which the Daimyo of Tsushima promised to pay tribute to the King of Joseon; in return, the Joseon court rewarded the Sō clan with preferential rights regarding trade between Japan and Korea.

In 1433, Sejong sent Kim Jongseo (hangul: 김종서, hanja: 金宗瑞), a prominent general, north to destroy the Jurchens (later known as the Manchus). Kim's military campaign captured several castles, pushed north, and expanded Korean territory, to the Songhua River. 4 counties and 6 garrisons (hangul: 사군육진 hanja: 四郡六鎭) were established to safeguard the people from the Jurchen.

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Science and Technology

Sejong is credited with great advances in science during his reign. He wanted to help farmers so he decided to create a farmer's handbook. The book—the Nongsa jikseol (hangul: 농사직설, hanja: 農事直說)—contained information about the different farming techniques that he told scientists to gather in different regions of Korea. These techniques were needed in order to maintain the newly adopted methods of intensive, continuous cultivation in Korean agriculture.

During his rule, Jang Yeong-sil (hangul: 장영실, hanja: 蔣英實) became known as a prominent inventor. Jang was naturally a creative and smart thinker as a young person. However, Jang was at the bottom of the social class. Sejong noticed Jang's skill and immediately called him to his court in Seoul. Upon giving Jang a government position and funding for his inventions, officials protested, believing a person from the lower classes should not rise to power among nobles. Sejong instead believed Jang merited support because of his ability. Jang created new significant designs for water clocks, armillary spheres, and sundials. In 1442, Jang made the world's first rain gauge named Cheugugi; it was the idea of Munjong, Sejong's son and heir. This model has not survived, since the oldest existing East Asian rain gauge is one made in 1770, during the reign period of King Yeongjo. According to the Daily Records of the Royal Secretariat (hangul: 승정원일기, hanja:承政院日記) King Yeongjo wanted to revive the glorious times of King Sejong the Great, and so read chronicles of Sejong's era. When he came across mention of a rain gauge, King Yeongjo ordered a reproduction. Since there is a mark of the Qing Dynasty ruler Qianlong (r. 1735–1796) of China, dated 1770, this Korean-designed rain gauge is sometimes misunderstood as having been imported from China.

Sejong also wanted to reform the Korean calendar system, which was at the time based upon the longitude of the Chinese capital. Sejong, for the first time in Korean history, had his astronomers create a calendar with the Joseon capital of Seoul as the primary meridian. This new system allowed Korean astronomers to accurately predict the timing of solar and lunar eclipses.

In the realm of traditional Korean medicine, two important treatises were written during the reign of Sejong. These were the Hyangyak jipseongbang and the Euibang yuchwi, which historian Kim Yongsik says represents 'Koreans' efforts to develop their own system of medical knowledge, distinct from that of China.

Outline of Sejong the Great (1397-1450)

HISTORIC PEOPLE

Sejong the Great (1397-1450)

Sejong the Great was the fourth king of Joseon-dynasty Korea. He created the Korean alphabet Hangul, encouraged advancements of scientific technology, and instituted many other efforts to stabilize and improve prosperity. He dispatched military campaigns to the north and instituted the Samin Policy to attract new settlers to the region. View Sejong the Great (1397-1450) »

Early Life: As a young prince, Sejong excelled in various studies and was favored by King Taejong over his two older brothers.

Achievements: King Sejong was an effective military planner. He created various military regulations to strengthen the safety of his kingdom, supported the advancement of Korean military technology, including cannon development.

Literature: Although most government officials and aristocrats opposed usage of hangul, lower classes embraced it, became literate, and were able to communicate with one another in writing.

Hangul: King Sejong the Great profoundly affected Korean history with his introduction of hangul, the native phonetic alphabet system for the Korean language.

Death and Legacy: The street Sejongno and the Sejong Center for the Performing Arts, both located in central Seoul, are named after King Sejong.

HISTORY

Sejong the Great (1397-1450)

Sejong the Great was the fourth king of Joseon-dynasty Korea. He created the Korean alphabet Hangul, encouraged advancements of scientific technology, and instituted many other efforts to stabilize and improve prosperity. He dispatched military campaigns to the north and instituted the Samin Policy to attract new settlers to the region.