Conversation so far:
What is Under the Banner of Heaven?
Under the Banner of Heaven: A Story of Violent Faith is a nonfiction book by author Jon Krakauer, first published in July 2003.
What was the focus of the book Under the Banner of Heaven by Jon Krakauer?
Under the Banner of Heaven by Jon Krakauer examines extremes of religious belief, specifically fundamentalist offshoots of Mormonism, polygamy, and a double-murder.

Question: What is the significance of the book?
Self-contained rewrite: What is the significance of the book Under the Banner of Heaven by Jon Krakauer?