What is the fine-grained topic of the following text: April 28, 2005  Robert Siegel talks with Middle East scholar William Polk about his new book, Understanding Iraq: The Whole Sweep of Iraqi History, from Genghis Khan's Mongols to the Ottoman Turks to the British Mandate to the American Occupation. Only return the topic.
A discussion about William Polk's new book, "Understanding Iraq: The Whole Sweep of Iraqi History".