National, ethnic and religious identity have been major drivers of deadly conflict both between and within states in the past, but looking to the future there are more reasons for optimism than caution. Contrary to common perceptions, cross-border wars declined dramatically after World War II, and civil wars and episodes of mass violence have declined dramatically since the end of the Cold War. Statistically at least, we seem to be learning at last to live together. But identity driven tensions still remain enemies of peace in a number of parts of the world, and complacency would be utterly inappropriate. Much still needs to be done if we are to end explosions of murderous nationalist sentiment, and above all genocide, ethnic cleansing and other mass atrocity crimes, once and for all.