In eight case studies by leading scholars in history, archaeology, business, economics, geography, and political science, the authors showcase the ?natural experiment? or ?comparative method??well-known in any science concerned with the past?on the discipline of human history. That means, according to the editors, ?comparing, preferably quantitatively and aided by statistical analyses, different systems that are similar in many respects, but that differ with respect to the factors whose influence one wishes to study.? The case studies in the book support two overall conclusions about the study of human history: First, historical comparisons have the potential for yielding insights that cannot be extracted from a single case study alone. Second, insofar as is possible, when one proposes a conclusion, one may be able to strengthen one?s conclusion by gathering quantitative evidence (or at least ranking one?s outcomes from big to small), and then by testing the conclusion?s validity statistically.