In response to Bryan Caplan's excellent post, "What If Lenin's Stroke Came [sic] Five Years Sooner," historian Susan, in the comments section writes:
I'm setting aside the major problem of engaging in historical counterfactuals, which as a historian I find problematic and uninteresting.
Yet, if she really means that, then she is restricting history to a simple recitation of facts. If we can't speculate about what would have happened if x hadn't happened or if politician y hadn't been been in charge, then what's left other than recitation of facts?
Fortunately, I'm not sure she means it. The reason is that she goes on to--engage in historical counterfactuals. She writes:
But given the general tenor of European thought post-1848, I find it hard to believe that no one would have attempted a Hitler- or Mussolini-like project in the 20th century, or that genocide would have been forestalled.
Of course, attempting and succeeding are two different things. But that's not my main point. My point is that Susan is saying that in the counterfactual world in which Hitler and Mussolini hadn't existed, there's a high probability that someone else in each country would have taken their place. She could be wrong and she could be right, but whichever she is, she is engaging in counterfactuals.