I'm have always had a fascination with military history and asian culture but my knowledge of both subjects is rather limited, so bare with me. I recently decided to start studying the history of the japanese samurai, particularly their weaponology. Having little former knowledge of the subject, but I had been led to believe that the katana and wakizashi where the traditional weapons of the samurai, even though they also used bows and spears. However, from what I have been reading the tachi and tanto seemed to be far more common as weapons up until the edo period. If I'm correct and the katana wakizashi combo didn't become common until the edo period, which was a very peaceful point in time, where katanas ever really a traditional wartime tool of the samurai? Is the perception of a samurai riding into battle with a katana and a wakizashi at his side just a western myth, or do I have my facts completely incorrect? If I'm incorrect, what time period did katanas become common place and when/why did they replace the tachi?
I'm by no means an expert on Japanese traditional warfare, but the idea of the katana being, as you say, a 'traditional wartime tool' does seem to a bit of a myth. The most prolific battlefield weapons were the bow and the spear (or naginata, a type of polearm), not the sword. Certainly not a relatively short sword like a tanto. That would be a terrible battlefield weapon.
Much of the katana's legend is tied up in what the weapon represented. It was much like a badge of office of the samurai class. Unfortunately, that has exxagerated the actual weapon's power a lot in recent times, up to the point where laymen believe it to be some kind of highly advanced, technological masterpiece that can cut literally anything. The reality is that it was a sword. A good sword, but still a sword, tied into a particular fighting style. With all the advantages and disadvantages that come with being a sword.
A super effective battlefield weapon it was not. If you're good with a naginata, which samurai undoubtedly would've been, you can stab your opponent in the face from 2 meters away, far outside of anyone's sword reach.
Things such as katanas, wakizashis, tantos, had more of a ceremonial/representative/personal defense during peacetime idea behind it. A naginata, like a halberd, is an incredibly powerful battlefield weapon, but you don't want to carry one around every day of your life. So you go for something more practical.
Building on top of /u/SchurkjeBoefje's answer, the katana being a mainstay of Japanese warfare is a myth. The katana did not even become a symbol of the samurai class until the Edo Period.
Before that, the true show of martial prowess was excellence in horseback archery.
In hand to hand combat, spears would be the first choice of any samurai, to the point that samurai would bring several spears to battle if they were able. Katanas were strictly a side arm.
Their place on the battlefield is lowered further with the introduction of firearms.
They only become a mainstay of samurai weapons under the Tokugawa government, who purposely allowed samurai to keep their swords because they offered a status symbol that was also non-threatening to the Tokugawa government, which controlled the manufacture of weapons like firearms very tightly.