Recent books demonstrate how terrorists make rational calculations when deciding whether to join the ranks; understanding their motivations will aid in stopping them. "Once you take terrorists to be rational actors, you need a theory about their rationale." Robert Pape, a political scientist at the University of Chicago, writes "What nearly all suicide terrorist attacks have in common is a specific secular and strategic goal: to compel modern democracies to withdraw military forces from territory that the terrorists consider to be their homeland."