 You have an ageing population with few kids, like in Japan, it shrinks. So what's going on where? And incorporated into that, too, would be the movements of people. And I came to the view that this was a really important phenomenon in so much of what's going on in the world, both historically and today, and perhaps a bit understudied. So it was worth writing some books on the subject. Thank you, Paul. Alex, 20th century history. I mean, history generally, but 20th century is your specialism. How come?