Korea as a nation is not typically regarded as having one of the strongest monarchies of the medieval world. Part of this is due to the largely Eurocentric history of the Middle Ages, as well as the fact that they competed against the mighty dynasties of medieval China and the ever-expanding Japanese Empire. However, one ruler stands out among his contemporaries, and for good reason: Sejong the Great. Being given the epithet the Great is a rare achievement for a monarch. Read on to discover how and why he gained this title.Sejongs Early LifeSejong the Great, posthumous portrait, 1973. Source: Academic.ruAs with many rulers during the Middle Ages, little is known about Sejongs childhood. However, we do know that his birth name was Yi To and that he was born on May 15, 1397. His father was Taejong, the third monarch of the Joseon Dynasty, and his mother was Queen Wongyeong. The young Yi Tos grandfather was King Taejo, the founder of the Joseon Dynasty, which would go on to rule Korea for another 400 years.Another interesting fact that we know about Yi Tos early life is that he was not born in Gyeongbokgung Palace, the main residence of Korean royalty. This is likely only because his father was not yet king at the time of his birth.Yis father arranged his marriage to Lady Sim of the Cheongsong Sim Clan, and she would later go on to rule as Queen Soheon. Aged 15 in 1412, Yi To was granted the title Grand Prince Chungnyeong, and three years later he fathered his first son, who would go on to rule as Munjong, the fifth monarch of the Joseon Dynasty.Sejongs Route to the ThroneTomb of Sejong the Great, photo by Kai Hendry. Source: FlickrSejong was actually the third-eldest son of Taejong, so would not naturally have been chosen to rule, as he had two older brothers.Grand Prince Yangnyeong was the eldest son, so he was expected to inherit the throne. However, Taejong realized that his eldest sons behavior was irrational and erratic, and, alongside court officials, recognized that Yangnyeong would have been an unsuitable ruler. Imagine how different European history could have looked if medieval monarchs adopted the same attitude!Eventually, Yangnyeong was dismissed as crown prince, and by mid-1418, officials were once again encouraging Taejong to select a new heir to the Korean throne.Taejong initially advocated for Yangnyeongs eldest son to become heir, as he would be the next in line, but after discussions with officials, they came to the conclusion that they needed a wise personunfortunately, Yangnyeongs son did not fit this category.The Veritable Records in Seoul National University. Source: Wikimedia CommonsThe Veritable Records of the Joseon Dynasty, the main primary source for this period, acknowledge that the Taejong gave a very measured response when asked why he was not choosing Yangnyeongs son: The father knows his sons best, as the king knows his subjects best.Following in his stead, the next obvious candidate was Taejongs second son, Grand Prince Hyoryeong. However, he viewed Hyoryeong to be too soft-natured, and he felt he would be unable to drink with and entertain Chinese Ming dignitaries.The baton then passed to Sejongperhaps a case of third-times-the-charm? Taejong saw Sejong as sharp, intelligent, politically savvy, and everything that a king should be. The court officials also welcomed this decision, later stating that he was their preferred choice. Although, whether this was simply to stay on the good side of Taejong, we do not know.On July 8, 1418, Sejong was pronounced crown prince of Joseon.Sejongs Early ReignPainting of Confucius, by Kan Sansetsu, 1632. Source: Wikimedia CommonsFollowing his decision to make Sejong Crown Prince, Taejong decided to abdicate just two months later. Sejongs reign officially began on September 18, 1418. However, despite his abdication, Taejong still retained various powers, such as having full control of the military and being able to make political decisions as king emeritus.However, unlike many medieval rulers, Sejong did not rue his fathers control. Instead, he sought to use his advice and did not challenge his authority. Taejong was not about to let his decisions backfire, though. He was a brutal ruler at times, and to avoid Queen Soheon gaining too much political power, he sought to leave her isolated, politically. He had her father executed on jumped-up charges of treason and had other members of her family exiled or made commoners.Religious TroublesPensive bodhisattva, Korea, mid-7th century. Source: The MET, New YorkReligion was a major point of contention during Sejongs reign. In Korea at the time, there were two primary religions: Confucianism and Buddhism. Confucianism had spread from mainland China and followed the teachings of the great ancient Chinese philosopher Confucius. Meanwhile, Buddhism had spread from the Indian subcontinent and had reached Korea around the 4th century CE.Sejong followed the rule of his father and most of the Joseon monarchs before him: promoting Confucianism and eradicating Buddhism.The way that Sejong managed to do this was not too dissimilar to King Henry VIIIs dissolution of the monasteries in 16th-century England. He reformed the land system entirely, seizing temple lands and redistributing them for development. As a result, Buddhist monks lost a lot of economic power, which naturally reduced their power to spread their religion. He forbade monks from entering the capital, Hanseong (modern-day Seoul), and he also reduced the seven schools of Buddhism to just two, limiting opportunities for Buddhists to practice their faith.In order to encourage Confucianism, Sejong performed government rites according to Confucian teachings and encouraged the general public to behave according to Confucianism.It was not just Confucians and Buddhists that Sejong dealt with, too. He completely eradicated Islam in the Korean peninsula, which had a lasting effect for centuries.In 1427, he issued a decree against the Huihui (Korean Muslims), who he felt had held special status since the Yuan Dynastys rule over Goryeo in the Korean peninsula in the last century. Sejong retorted by banning Muslim headgear and closing down their ceremonial mosque in Kaesong, forcing them to worship in line with Korean religious practices. In the entire Joseon Era from then onwards (which lasted until 1910) no further records of Muslims existed, suggesting that Sejong had effectively ended Islam in Korea for the next 400 years.Military Expansionism Under Sejong the GreatTsushima Island, photo by Nichika Sakurai. Source: UnsplashThe most famous military foray in Sejongs reign was the final military campaign of Tsushima. This is known as the Gihae Expedition in Korea and the ei Invasion in Japan which says a lot.From June 20 to July 3, 1419, Korean troops were sent to deal with Japanese pirates based off Tsushima, an island about halfway between Japan and Korea in the Korea Strait.245 Japanese were killed or executed during the invasion, a further 110 were captured, while 180 Koreans were killed. A truce was made in July 1419 and the Joseon army returned to the Korean peninsula.The only other major military expansion during Sejong the Greats reign was when he conquered the Jurchens, further north in the far north of modern-day North Korea and southern China. This expedition was a success, and the Korean forces captured numerous fortresses, which helped to expand Sejongs territory to the banks of the Songhua River.Science and Technology Under Sejong the GreatSujeongjeon in the Gyeongbokgung Palace, a building once used by the Hall of Worthies. Source: Wikimedia CommonsAs well as the military advancements and religious reforms during his tenure as king of Korea, Sejong was also involved in some huge technological advancements.He was a big believer in promoting science, and in 1420 established the Hall of Worthies within the Gyeongbok Palace, which was a place where the finest thinkers in the kingdom were encouraged to share their ideas. The government also offered grants for budding young scholars to attend.In 1428, Sejong ordered 1,000 copies of a farmers handbook to be published, and in 1429 he published Nongsa Jikseol, which literally translates as Straight Talk on Farming, a compilation on farming methods designed to suit Koreas climate and soil types.The inventor Jang Yeong-Sil was appointed as a court technician by Sejong, and he remained with him for much of his career. In 1434, Jang invented a new type of printing press, powered by copper-zinc and lead-tin alloys, which allegedly worked twice as fast as the previous model, allowing items to be distributed even quicker.Another scientific reform that Sejong ordered during his reign was the redevelopment of the Korean calendar. Initially, it had been based on the longitude of the Chinese capital, but Sejong instead ordered it to use Hanseong (the Joseon capital) as its primary meridian. This in turn allowed Joseon astronomers to accurately predict lunar and solar eclipses.Popular Reforms Under Sejong the GreatFlag of the King of Joseon, c. 1882. Source: Wikimedia CommonsSejong was well ahead of the trend when it came to womens rights. He introduced 100 days of maternity leave for serfs in 1426, which was extended by one month prior to childbirth in 1430. In 1434, he also granted the husbands of pregnant women 30 days of paternity leave.Furthermore, he also realized how important agricultural output was to the Korean economy, so he favored farmers greatly. One notable thing he did was allow them to pay less tax in times of hardship, due to adverse weather conditions ruining crop yields. It was once even claimed that when the palace had a surplus of food, Sejong ordered it to be distributed among the poor.The Development of the HangulHangul on Korean Papers in Isadong. Source: Wikimedia CommonsPerhaps the biggest achievement in Sejongs reign, though, was the creation, introduction, and development of the Hangulthe modern Korean alphabet.It is likely that those in the Hall of Worthies developed the Hangul, but even if this was the case, they were under the instruction of Sejong to do soso really, he was responsible for the advancement of the Korean language.Before the Hangul, most Koreans wrote in classical Chinese, so most Korean documents prior to Sejongs reign were written in Chinese. Not only did the introduction of Hangul help to transform Korean history, but it helped to give the Korean people a sense of identity. This worked in the favor of all Korean peoplemost of the poor people in medieval Korean society were illiterate, as they had not received the level of education necessary to learn classical Chinese.Therefore, another purpose of the introduction of Hangul was to promote literacy rates throughout Korea with a language and alphabet system that everyone could understand.Hangul was completed in 1443 and published in 1446, but not without backlash and controversy.Many of the Korean nobility opposed giving peasants the ability to read and write, feeling that their positions could be under threat and that they would be able to find loopholes in the law. Fortunately, Sejong ignored them and proceeded to develop Hangul.After his death, many nobles refused to use Hangul and continued to communicate in classical Chinese, to distinguish themselves. Hangul survived this petty behavior, while other kings outlawed it and then reintroduced it in the following centuries. By 1945, Hangul was the official written language of Korea.Sejongs Death and LegacyThe tomb of Sejong the Great. Source: Wikimedia CommonsFor a number of years, Sejongs health had been declining. In 1439, his health worsened, and by 1442, his eldest son, Yi Hyang, served as regent in his fathers stead.Sejong eventually died on April 8, 1450.He was buried alongside his wife who had died four years earlier, and his tomb now lies in Yeoju, South Korea.The legacy that Sejong left behind is unquestionable. He was, without a doubt, the greatest ruler of medieval Korea, and arguably the greatest-ever Korean monarch.From his scientific and technological advancements such as the introduction of new printing presses, to the military campaigns against the Japanese, and the introduction of the Hangul, Sejong certainly deserves to be called the Great.While he is remembered more fondly in South Korea than in North Korea today, one thing can be said about him: he did more to unite Korea as a whole than many of his modern-day successors have.