First there was The Weird Forest which was full of magic-like stuff. It is not commonly agreed upon whether this was magic as we now know it or if it was more like a different kind of pure life force.
Due to the spring cleaning of the Underworld, magic now sometimes has its own opinions. Magic is mixed with age old dead souls.
Magic becomes uncontrollable due to its infestation of souls and spirits of the ancient dead. Anima did not quite completely cause it, but she surely did not want to prevent it.