In 1392, the Goryeo kingdom was overthrown and the state of Joseon dynasty was founded. The founder of the dynasty, Taejong made several attempts to bring upon improvements in the prevailing monetary system but they were not a success initially. The attempts include issuing Korean paper currency and issuing coins instead of importing them from China. The coins issued in Korean being unsuccessful led to the issuance of a standardized note made of black mulberry bark called Jeohwa (저화/楮貨), that was used in place of coins. Bronze coins were not cast again until the year 1423 during the reign of King Sejong. These coins had the inscription 朝鮮通寶 (Chosun Tongbo "Chosun currency"). The coins that were minted in the 17th century came out to be a success at last and as a result, 24 mints were established throughout Korea. Coinage formed a major part of the exchange system after this time. In 1633, "mun" was made the main currency of Korea and copper and bronze coins were issued denominated in this currency unit. It prevailed till 1892 when "yang" took over as the main currency. Yang was the first currency that used decimal system as it was divided in 100 equal fun, though it did not last long.