The problem with fighting zombies is that they are undead – that is, they move with surprising speed, even though they are relatively slow.
They have endless endurance, and superhuman strength. They feel no cold, no heat, no fear, no doubt, no fatigue and no pain. They remember nothing, they have an uncanny ability to find living flesh, especially live man, even when missing sensory organs (eyes, ears, etc) .
When encountering the zombie horde for the first time, samurai – great warriors of Japan – would follow their normal battlefield instincts, which was to face off with a single foe and after he was defeated, move to the next.
This ended in tragedy for the many samurai who encountered the zombie horde for the first time, as they were easily inundated within moments, even though they dispatched many zombies. The war lords of Japan ceased sacrificing their best samurai to the zombie horde, and instead sent teams of shinobi – ninja warriors – whose effectiveness as killers and strange arcane powers made them more successful at stopping the zombie horde than any other factor.