History may appear logical and even inevitable: Things happened because they had to. But when you go back to examine the great turning points of the past, you quickly discover how choices, chances, and accidents played a huge rule in making the world we know today. Politicians, writers, explorers, and ordinary people all make choices that shape history. But examining the moments that define our history raises an important question: What if things had gone differently?

Historians have a term for this type of speculation. A "counterfactual" history imagines a different person, a different decision, different luck in a critical moment-and the way a small change could have transformed history as we know it. What if Christopher Columbus never got the money to sail in 1492? What if the Union lost the Battle of Gettysburg? Or President John F. Kennedy escaped assassination?

As you'll learn, a well-constructed counterfactual is about more than flipping a switch or taking a guess. Historians look for moments of "contingency"-times when something unlikely happened or when events turned on a moment that could have gone either way. What happens when you take away favorable weather conditions or delay an event by 15 minutes?

Accompanied by a selection of guests, Professor Jortner takes you through a mind-bending exploration of the history that could have been. Captivating storytellers and imaginative thinkers, these experts show how history is contingent on split-second decisions, near misses, and sheer dumb luck. By reflecting on what didn't happen, 10 Great What-Ifs of American History gives you new insights on what did happen-and the impact on our world today.