In the Foundation Trilogy of novels, Isaac Asimov imagines a future where social scientists develop the field of "psychohistory" which allows them to predict the future course of human civilization. Zoom in closer and human lives still follow a totally unpredictable trajectory. But when summed together, the combined effect of (more or less) random individual choices is a non-random, predictable macro outcome.
The spanner in the works is an exceptional person whose transcendent influence can change the course of history in ways psychohistory cannot predict.
"They remain, uniquely, a thrilling tale about how self-knowledge—an understanding of how our own society works—can change history for the better. And they’re every bit as inspirational now as they were when I ﬁrst read them, three-quarters of my life ago."
What if instead of looking forward to improving society, we look back at the history of human suffering? The distinction between events caused by the macro forces of history and contingent events that would not have occurred but for the free will of one individual is a real one.
For example, upon testing the first atomic bomb, Robert Oppenheimer is said to have quoted Hindu scripture: "I am become death, the destroyer of worlds." But this is egotistical. Someone was bound to develop the bomb, and Oppenheimer played, at most, a small role in determining the exact time and place.
On the other hand, President Truman's decision to drop the bomb seems underdetermined. Even if it is true that the use of atomic weapons became inevitable once they were developed (and I don't think it is), they would not have been used at that time, in that context, with that result, but for Harry Truman.
Thus, the death and destruction of Hiroshima should figure in our moral judgment of Truman in a way that it doesn't for Oppenheimer.
What happens when we apply this distinction to other historical episodes of mass suffering? Are some instances of human suffering predetermined by historical forces in contrast to other contingent events where widespread suffering is down to a single individual who was free to choose otherwise? If so, are those individuals more morally culpable than those who simply ran herd over historical forces?