Since the Three Kingdoms Period, Koreans have written in Idu and Gugyeol script. Even though Idu was able to express Korean, it was unable to freely write Korean, thus Chinese character education had to be preceded even when Idu script wasn’t perfect. This inconvenience exacerbated the emergence of new easy-to-learn and easy-to-write characters without using Chinese.
This ideology was particularly prominent during the reign of King Sejong, because after Taejong enthroned Sejong, one of the major things Joseon needed to improve on was the stability of foods, however, most of the farmers were illiterates, There for they didn’t have much knowledge about farming. King Sejong realized the urgency of an easier language after he published a book about farming, but most couldn’t read it.
And finally, the literati revolution happened in the lunar calendar of 1443. The purpose of creating Hunminjeongeum is to make it easy to use in everyday life because the difference in Chinese and Korean made it hard to use, and secondly because we do not have unique characters, thus it's impossible to express all aspects of Korean."Hunminjeongeum" means "the right sound to teach the people”. It was optimized for Korean to overcome the difficulties of relying on Chinese characters.
When it was first made, there were 28 alphabets and a separate symbol for intonation expression, but now the four letters ᅀ, ᅌ, ᅙ and · are not used anymore, currently, only 24 letters are used. (The pronunciation of · still remains in some places, including Jeju Island.)
Over the next few hundred years, people mainly used Chinese characters rather than Hangul, but the lower class and women who could not learn Chinese characters, wrote in Hangul to send letters or a contract, and in the royal palace, they wrote in hangul for documents exchanged between women.
Hangul, which was first distributed as 'Hunminjeongeum', was called 'Unmun' during the Joseon Dynasty. This is due to the fact that the inscription "Sangchinjebun Sippalja" in the Annals of King Sejong, everything except Hanja was called "Unmun." It was used by the royal court, some Yang-ban, and most citizens.
Hangul started spreading rapidly in the 1500s, it was because Hunminjeongeum became a required test for officials of Joseon In April 1445 (the 27th year of King Sejong's reign). Since then, Hunminjeongeum has been written in documents of the private sector and the government. even used by potters, who were at the level of slaves in rural areas, half a century later.