Why do we wonder "what if?" about the past? In his pathbreaking, two-volume study, Gavriel Rosenfeld provides the first comprehensive examination of counterfactual history from its inception to the present day. Surveying more than three millennia of western history, Rosenfeld challenges the longstanding claim that historical speculation is contrary to legitimate historical inquiry. He documents the astounding ubiquity of counterfactual thought in the western tradition, showing how historians, theologians, politicians, philosophers, journalists, and novelists wondered "what if?" about the events of their day. In Volume II, Rosenfeld surveys the two centuries between 1800 and the present, examining hundreds of classic texts - from Napoleon Bonaparte's Memoirs to Philip K. Dick's The Man in the High Castle - to shed light on the missed opportunities and close calls of western history. By showing how counterfactual history has gained an increasingly prominent place in western culture, Rosenfeld demonstrates that imagining what might have happened is essential for understanding what did.