In Emily Dickinson's poem (titled by the first line of the poem given many of her poems were untitled and publishers needed a way to "name" them after her death) "Witchcraft was hung in history" allows a reader to see the importance of two very different ideas.
First, Dickinson is referring to the fact that witchcraft has a place in history which many are familiar with. Given the tumultuous history in England and America with the witch hysteria, Dickinson is referring to the fact that people still speak of the fact that the trials of many people and the deaths of many more was so tragic that "our" history has been hung much like the many people who were hung based upon their accusations and guilty verdicts regarding their being witches.
Second, Dickinson recognizes the fact that even though witchcraft has been hung in history, it is still relevant for her and "us." Given that Dickinson was a Romantic poet, her poetry was riddled with images of nature and imagination. Here, Dickinson admits that for people to live they need to accept and recognize that "we" all need a little magic and mysticism in "our" lives.
Therefore, Dickinson is simply stating that witchcraft has not remained upon the wall. Instead, it exists around all of us, if we look for it or not. It, witchcraft, no longer holds the taboos it did in the past. It can be brought down off the wall.