Some central questions in the natural and social sciences can't be answered by controlled laboratory experiments, often considered to be the hallmark of the scientific method. This impossibility holds for any science concerned with the past. In addition, many manipulative experiments, while possible, would be considered immoral or illegal. One has to devise other methods of observing, describing, and explaining the world.

In the historical disciplines, a fruitful approach has been to use natural experiments or the comparative method. This book consists of eight comparative studies...