Is The Gift of Sarah Barker a fiction or nonfiction book?

The community Yolen creates, although fictional, is based upon fact. Yolen explores her themes in terms of the history of the United Society of Believers in the First and Second Appearing of Christ, commonly known as the Shakers. The Shakers flourished from Revolutionary times in America to the 1860s, then went into a period of decline. The Shakers eventually disappeared because they rejected marriage and childbearing.