In the times of the samurai before the Meiji Restoration there were hundreds of schools of "killing orientated" swordsmanship. The names kenjutsu, kendo etc were all used for it, allthough different terms were more popular with different people at different times.
The vague (and here quite over-generalised) distincion that kendo is a competitive sport, kenjutsu is old-style "killing orientated" swordsmanship and iaido is a mostly meditative thing is a much more modern thing. As far as I know, the swordsmanship that the samurai used is most similar to koryu kenjutsu out of all the current "systems."
Feel free to correct me if I'm mistaking on anything.