In Peyote and the Yankton Sioux, Thomas Constantine Maroukis focuses on Yankton Sioux spiritual leader Sam Necklace, tracing his family's history for seven generations to show how Necklace and his family shaped and were shaped by the Native American Church. Sam Necklace was chief priest of the Yankton Sioux Native American Church from 1929 to 1949, and four succeeding generations of his family have been members. As chief priest, Necklace helped firmly establish Peyote religion among the Yanktons, thus maintaining cultural and spiritual autonomy even when the U.S. government denied them, and American Indians generally, political and economic self-determination. A sacred plant long considered of divine origin by Mesoamericans, peyote's ritual use spread northward through the American Southwest near the end of the nineteenth century. According to Native beliefs, peyote enabled human beings to communicate with the Creator. Because the message of peyotism resonated with Yankton pre-reservation beliefs and, at the same time, had parallels with Christianity, Sam Necklace and many other Yanktons supported its acceptance. The Yankton Sioux were among the first in the northern plains to adopt the Peyote religion, which they saw as an essential corpus of spiritual truths. Contrary to what some scholars have claimed, Maroukis explains that Peyotism was adopted because of its vision-inducing effects. The Native American Church accepts peyote as a powerful medicine - a gift from God with the power to heal.