an interview with Sir David Cannadine on his book, The Undivided Past: Humanity Beyond Our Differences. He made a good point that so much of what we see and hear about the world stresses conflict, but much of human history and most of human institutions seem to focus on cooperation and communication -- the good news seems not to be newsworthy.
In his book he looks at six topics: religion, nation, class, gender, race and "civilization", noting that these are factors by which people tend to define themselves, and that different people at different times have stressed each as "the defining basis" for self-identification. (Religion as the basis for Christian-Muslim conflict, etc.)
He notes that "nation" is a relatively new organizing concept. I suppose it has replaced tribe for much of the world, although tribalism seems still important in some places. Clearly we think of nationalism as an underlying element in the great conflicts of the 20th century.
In the interview he mentioned that "empire" was something he considered as a possible chapter subject, but did not ultimately choose. Multi-ethnic empires and multi-racial empires were clearly different than nation-states, and we certainly saw empires fighting each other for a long, long time.
But I wondered whether age might not be considered as also one of those ways in which we define ourselves -- think of Shakespeare's seven ages of man. Today, at least, we clearly think of childhood as different than working age, or than old age. Think of the Young Turks waiting for their turn at the seats of power.
I also wonder if there is not an emerging division between "modern", educated people who tend to value scientific knowledge and adapt new technologies quickly versus "traditional" people with less formal education, who tend to value traditional knowledge and adapt new technologies less quickly.