Witches: Chronicle of a Massacre

In 1609, Henry IV sent Inquisition judge Pierre de Lancre to the French Basque Country to investigate witchcraft. In the trials, 80 people were sentenced to death at the stake. Between the 15th and 17th centuries, a total of between 40,000 and 60,000 people fell victim to such waves of persecution in Europe. How can this phenomenon be explained?