"Memoirs of Extraordinary Popular Delusions — Volume 2" by Charles Mackay is a study of crowd psychology first published in 1841. This volume examines humanity's most fervent collective manias, from the religious fervor of the Crusades to the deadly witch trials that swept through Europe. Mackay chronicles how thousands fell victim to mass hysteria, how neighbors turned against each other with flimsy evidence, and how entire societies succumbed to irrational beliefs. Through vivid storytelling, he reveals the dangerous power of popular delusion across centuries. (This is an automatically generated summary.)