From the introduction:
"Aside from morbid fascination, is there any reason to know the one hundred highest body counts of history? Four reasons come to mind:
"First, things that happen to a lot of people are usually more important than things that happen to only a few people....
"Second, killing a person is the most you can do to him....
"Therefore, just by default, my one hundred multicides had a maximum impact on an enormous number of people. Without too much debate, I can easily label these to be among history's most significant events.
"....
"A third reason to consider is that we sometimes forget the human impact of historic events....
"The fourth and certainly most practical reason to gather body counts is for risk assessment and problem solving. If we study history to avoid repeating the mistakes of the past, it helps to know what those mistakes were, and that includes ALL of the mistakes, not just the ones that support certain pet ideas." pg. xvi

"Despite my skepticism about any common thread running through all one hundred atrocities, I still found some interesting tendencies. Let me share with you the three biggest lessons I learned while working on this list:
"1. Chaos is deadlier than tyranny. More of these multicides result from the break-down of authority rather than the exercise of authority....
"2. The world is very disorganized. Power structures tend to be informal and temporary.... Most wars don't start neatly with declarations and mobilizations and end with surrenders and treaties.... Most nations are not as neatly delineated as you might expect....
"3. War kills more civilians than soldiers. In fact, the army is usually the safest place to be during a war...." pg. xvii