Japanese double edged swords, known as tsurugi, have been used in Japan ever since the Yayoi period (from 800~300 B.C. to 300 A.D). In fact, the most famous sword in Japanese mythology, Ame no Murakumo, is double-edged. They continued to see prevalent use in the succeeding Yamato Empire. The Yamato national army was based off of China and both straight swords (tsurugi) and sabres (katana) imitated Chinese design at the time. They were primarily used by infantrymen who carried large shields.

The downfall of the traditional Yamato national army came at the hands of the Emishi: Japanese aboriginals whose expertise was horse archery. The Yamato army was unable to cope with the hit-and-run tactics of the horse archers and were soundly defeated. As a result, their prestige waned and the army was disbanded. The national army was replaced by regional warlords living in the fringes of the Empire (Kanto and Tohoku) later known as Samurai. These samurai were horse archers, like the aboriginals, and were successful in quelling them: earning the prestige that the Yamato army had lost.

So much was the clout of the Samurai that in the ensuing Heian period, Samurai would acquire a monopoly on warfare in Japan. For the next three hundred years, war would be fought exclusively by Samurai. The Samurai at the time were primarily horse archers and so preferred the tachi, which was suited for slashing on horseback. Straight swords and shields were considered infantrymen weapons, and so were not used. During the Samurai monopoly, infantry was neglected. They were seen as unnecessary as warfare devolved into ritualistic horseback duels. Because of this, infantry started to disappear from Japanese warfare. Straight swords and shields faded from use, nearly never to be seen again.

All of this changed when the Mongols invaded Japan during the 13th Century. The invaders changed warfare in Japan: the Samurai were awakened to the realities of combat and had to do away with their ritualistic combat. The samurai had to fight on foot and peasants were brought out as infantry. In the aftermath of the Mongol invasions, the Samurai realized that their swords were ill suited to infantry combat. The new sword that they conceived to replace them, the uchigatana, was based off of its tachi predecessor. Hence, even as Samurai became infantry based and increasingly armoured, sabres were still the sword of choice.

Even as infantrymen, however, the uchigatana would fail to see much use in the hands of the samurai. They were not primarily swordsmen and so the katana was merely a sidearm. The weapons of choice were the pike and bow, later replaced with pike and arquebus during the 16th Century. Due to their expensive nature and craftsmanship, however, the katana retained an importance as a status symbol.