There is a large and growing body of evidence in anthropological and historical literature that historical European-style witchcraft was a form of shamanism. There are essentially three lines of argument here: One, espoused by Éva Pócs and Carlo Ginsburg, connects medieval and Early Modern practices to pre-Christian religious beliefs, mostly in eastern Europe where conversion happened later and the lines of connection are easier to trace (but with implications for other regions). The second, presented by Claude Lecouteux in his book Witches, Werewolves, and Fairies, compares accounts of supernatural experiences during the medieval period (including transcripts from witchcraft and werewolf trials) in Germany to the relatively undisturbed shamanic practices further north. The third, presented by Emma Wilby in her book Cunning Folk and Familiar Spirits, puts the experiences and practices of Early Modern witches into a context of world-wide shamanic practice.
To be clear, the definition of “shaman” in use here is an anthropological one. The word originates from the Tungus language of Siberia, and has been somewhat misapplied to the religious beliefs and practices of Native Americans (which are quite diverse; some are certainly shamanistic, others not so much). A shaman in this context is a magical practitioner who works with the help of spirits, usually (though not always) on behalf of or to the benefit of his or her human community, by means of healing, divination, and the like. Shamanic experiences world-wide share some general characteristics: the “call” in the form of a traumatic personal experience and/or a visitation by spirits, the formation of a strong bond (often including an agreement, pact, or spirit marriage) between the new shaman and one or more helping spirits, and a working relationship with those spirits, frequently characterized by ritual invocation and spirit flight or trance states to achieve specific goals.