Sejong the Great was the fourth king of Joseon. Born with family name Yi , given name Do, family origin Jeonju, sobriquet Wonjung. Posthumous name is Sejong. Posthumous title, abbreviated, is JangHun Great King, and official title is Sejong Jangheon Yeongmun Yemu Inseong Myeonghyo Daewang (세종 장헌 영문 예무 인성 명효 대왕; 世宗 莊憲 英文 睿武 仁聖 明孝 大王). He was the third son between King Taejong and Queen-Consort Min. He was designated as heir-apparent, Grand Prince, after his older brother Jae was stripped of his title. He ascended to the throne in 1418. During the first four years of his reign, Taejong governed as regent, and this was when his father-in-law, Shim Ohn, and his close associates were executed.
Sejong reinforced Confucian policies and executed major legal amendments (공법; 貢法). He also oversaw the creation of Hangul, encouraged advancements of scientific technology, and instituted many other efforts to stabilize and improve prosperity. He dispatched military campaigns to the north and installed Samin Policy (사민정책; 徙民政策) to attract new settlers to the region. To the south, he subjugated Japanese raiders and captured Tsushima Island.
During his reign from 1418 to 1450, he governed from 1418 to 1442 and governed as regent with his son Grand Prince MoonJong until his death in either 1442 or 1450.
Sejong is one of only two Korean rulers posthumously honored with the appellation "the Great", the other being Gwanggaeto the Great of Goguryeo.
Taejong consolidated the power of the monarchy by eliminating political opponents such as government ministers who had contributed to the founding of Joseon. Taejong's actions provided Sejong with unchallenged political authority during his reign.
Sejong was born on May 15, 1397, the third son of King Taejong. When he was twelve, he became Grand Prince Choong-Nyung. As a young prince, Sejong excelled in various studies and was favored by King Taejong over his two older brothers.
As the third son of Taejong, Sejong's ascension to the throne was unique. Taejong's eldest son, Yangnyeong (양녕대군), was named heir apparent in 1404. However, Yangnyeong was free spirited nature as well as his preference for hunting and leisure activities resulted in Yangnyeong being removed from the position of heir apparent in June of 1418. Though it is said that Yangnyeong abdicated in favor of his younger brother there are no definitive records regarding Yangnyeong's removal. Taejong's second son Grand Prince Hyo-Ryung upon the elevation of his younger brother Sejong became a monk.
Following the removal of Yangnyeong as heir apparent Taejong moved quickly to secure his youngest son's position as heir apparent. The government was purged of those officials who had disagreed with the removal of Yangnyeong as heir apparent. In August of 1418 Taejong abdicated in favor of Sejong. However, even in retirement Taejong continued to influence government policy. Sejong's surprising political savvy and creativity did not become apparent until after Taejong's death in 1422.
Starting Politics Based on Confucianism
King Sejong revolutionized government by appointing people throughout different social classes to 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 social norm. He also published some books about Confucianism.
At first, he suppressed Buddhism, but he alleviated his action by building temples and accepting Buddhism by making a test to become a monk (Seung-gwa).
In relationship with Ming, he made some successful agreement that benefitted Chosun. In relationship with Jurchen people, he installed 4-goon(郡) and 6-jin(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 Manchu. Kim's military campaign captured several castles, pushed north, and restored Korean territory, to the Songhua River. Four forts and six posts were established (hangul: 사군육진 hanja: 四郡六鎭) to safeguard the people from Jurchen nomads.
Science and Technology
Sejong is credited with technological advances 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. Taejong, the father of 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. However, his most impressive invention came in 1442, the world's first rain gauge, named Cheugugi (source?); 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 Korean 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.' They were now separated.
Sejong supported literature, and encouraged high class officials and scholars to study at the court. King Sejong created the written language of hangul and announced it to the Korean people in the Hunminjeongeum (Hangul:훈민정음, Hanja: 訓民正音), meaning 'The verbally right sounds meant to teach the people.'
Sejong depended on the agricultural produce of Joseon's farmers, so he allowed them to pay more or less tax according to fluctuations of economic prosperity or hard times. Because of this, farmers could worry less about tax quotas and work instead at surviving and selling their crops. Once the palace had a significant surplus of food, King Sejong then distributed food to poor peasants or farmers who needed it. In 1429 Nongsa-jikseol (hangul: 농사직설, hanja: 農事直說) was compiled under the supervision of King Sejong. It was the first book about Korean farming, dealing with agricultural subjects such as planting, harvesting, and soil treatment.
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.
Sejong's personal writings are also highly regarded. He composed the famous Yongbi Eocheon Ga ("Songs of Flying Dragons", 1445), Seokbo Sangjeol ("Episodes from the Life of Buddha", July 1447), Worin Cheon-gang Jigok ("Songs of the Moon Shining on a Thousand Rivers", July 1447), and the reference Dongguk Jeong-un ("Dictionary of Proper Sino-Korean Pronunciation", September 1447).
In 1420 Sejong established the Hall of Worthies (집현전; 集賢殿; Jiphyeonjeon) at the Gyeongbokgung Palace. It consisted of scholars selected by the king. The Hall participated in various scholarly endeavors, of which the best known may be the compilation of the Hunmin Jeongeum.
King Sejong the Great profoundly affected Korean history with his introduction of hangul, the native phonetic alphabet system for the Korean language.
Before the creation of Hangul, only members of the highest class were literate (hanja was typically used to write Korean by using adapted Chinese characters, while Hanmun was sometimes used to write court documents in classical Chinese). One would have to learn the quite complex hanja characters in order to read and write Korean. Further, despite modifications to the Chinese characters, hanja could prove cumbersome when transcribing the Korean language, due to considerable differences in grammar and sentence order. While creating the alphabet, King Sejong encountered opposition of courtiers.
King Sejong presided over the introduction of the 28-letter Korean alphabet, with the explicit goal being that Koreans from all classes would read and write. Each hangul letter is based on a simplified diagram of the patterns made by the mouth, tongue and teeth when making the sound related to the character. Morphemes are built by writing the characters in syllabic blocks. His intention was to establish a cultural identity for Korea through its unique script. The blocks of letters are then strung together linearly.
First published in 1446, anyone could learn Hangul in a matter of days. Persons previously unfamiliar with Hangul can typically pronounce Korean script accurately after only a few hours study.