sending swordsmiths to Japan and inviting Japanese swordsmiths to Korea. According to the record of June 1, 1430 in the Veritable Records of the Joseon Dynasty, a Korean swordsmith who went to Japan and mastered the method of making Japanese swords presented a Japanese sword to the King of Korea and was rewarded for the excellent work which was no different from the swords made by the Japanese. Traditionally, yumi (bows) were the main weapon of war in Japan, and tachi and naginata were for close combat. The Ōnin War in the late 15th century in the Muromachi period expanded into a large-scale domestic war, in which employed farmers called ashigaru were mobilized in large numbers. They fought on foot using katana shorter than tachi. In the Sengoku period (period of warring states) in the late Muromachi period, the war became bigger; ashigaru fought in a close formation using yari (spears) lent to them. Furthermore, in the late 16th century, tanegashima (muskets) were introduced from Portugal, and Japanese swordsmiths mass-produced improved products, with ashigaru fighting with leased guns. On the battlefield in Japan, guns and spears became main weapons in addition to bows. Due to the changes in fighting styles in these wars, the tachi and naginata became obsolete among samurai, and the katana, which was easy to carry, became the mainstream. The dazzling-looking tachi gradually became a symbol of the authority of high-ranking samurai. From the 15th century, low-quality swords were mass-produced under the influence of the large-scale war. These swords, along with spears, were lent to recruited farmers called ashigaru, while swords were exported. Such mass-produced swords are called kazuuchimono, and swordsmiths of the Bisen school and Mino school produced them by division of labor. The export of Japanese sword reached its height during the Muromachi period—at least 200,000 swords were shipped to Ming Dynasty China in official trade in an attempt to soak-up the production of Japanese weapons and make it harder for pirates in the area to arm. In the Ming Dynasty of China, Japanese swords and their tactics were studied to repel pirates, and wodao and miaodao were developed based on Japanese swords. From this period, the tang (nakago) of many old tachi were cut and shortened into katana. This modification is called suriage. For example, many of the tachi Masamune forged during the Kamakura period were converted into katana, so his only existing works