A book about the related, long-term trend of decrease violence explained with different angels: https://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Nature h

A book about the related, long-term trend of decrease violence explained with different angels: https://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Nature https://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Natur... (Religious extremists, totalitarian regimes notwithstanding.)