Counterfactual history is the game of attempting to imagine what would have resulted had different decisions been taken by the historical actors and to understand how history, personal, corporate or history with a capital H, would have turned out if certain decisions had been made different from those that had actually been made. Thus, the importance of relative events can be analyzed.

Back in 1931, Winston Churchill imagined how different the world would have been if General Lee would have been if he would have won the battle of Gettysburg.

Counterfactual history has led to the theory of contingency history that supports the idea that history is not deterministic but that small events are determinant in the direction that history takes.