"Counterfactual" games are fun. I often bring up such to stimulate thinking. IF the Persians had defeated and destroyed the Greeks? IF Hitler had developed the atomic bomb before we did? IF the British and captured/defeated Washington on Long Island? My favorite (since Civil War is my forte) is IF the "lost orders" that led to the stalemate at Antietam had not be "lost", nothing could have stopped Bobby Lee. What is YOUR favorite event that, if turned on its head, you find most intriguing?