As long as your ideology identifies the main source of the world's ills as a definable group, it opens the world up to genocide.

Most wars are not fought over shortages of resources such as food and water, but rather over conquest, revenge, and ideology.

The European wars of religion were more deadly than the First World War, proportionally speaking, and in the range of the Second World War in Europe. The Inquisition, the persecution of heretics and infidels and witches, they racked up pretty high death tolls.

Reading is a technology for perspective-taking. When someone else's thoughts are in your head, you are observing the world from that person's vantage point.

'Capitalism' is a dirty word for many intellectuals, but there are a number of studies showing that open economies and free trade are negatively correlated with genocide and war.

The decline of violence isn't a steady inclined plane from an original state of maximal and universal bloodshed. Technology, ideology, and social and cultural changes periodically throw out new forms of violence for humanity to contend with.