A collective memory is a representation of the past that is shared by members of a group. We investigated similarities and differences in the collective memories of younger and older adults for three major wars in U.S. history (the Civil War, World War II, and the Iraq War). Both groups were alive during the recent Iraq War, but only the older subjects were alive during World War II, and both groups learned about the Civil War from historical sources. Subjects recalled the 10 most important events that occurred during each war and then evaluated the emotional valence, the relative importance, and their level of knowledge for each event. They also estimated the percentage of people that would share their memory of each event within their age group and the other age group. Although most historical events were recalled by fewer than 25 % of subjects, younger and older adults commonly recalled a core set of events for each war that conform to a narrative structure that may be fundamental to collective remembering. Younger adults showed greater consensus in the events that they recalled for all three wars, relative to older adults, but there was less consensus in both groups for the Iraq War. Whereas younger adults recalled more specific events of short duration, older adults recalled more extended and summarized events of long duration. Our study shows that collective memories can be studied empirically and can differ depending on whether the events are experienced personally or learned from historical sources.