This was an interesting panel which discussed various pivotal historical events that, in retrospect, must have been influenced by time travelers due to their otherwise somewhat inexplicable nature, particularly in terms of some of the "coincidences" that allowed them to come to pass.
Much of the discussion focused around events during the American Civil War. (For some reason, this period seems to be a favorite for alternate history aficionados.) The key points centered chiefly on political and military leaders.
At the end, unfortunately too late to be discussed at length, came the question about key scientific, technological and sociological changes that might have proven to be pivotal. I would have found this line of discussion particularly intriguing. Alas, it was too late and was barely touched upon.