We're living in unusual times, with political history being made every week, the seemingly imminent collapse of a certain global super power and serious existential crises, or just crises, on the horizon.  "Once you pull on the thread of collapse, the entire tapestry of history begins to unravel" writes Luke Kemp. So what can we learn from looking at the collapse of past societies?

• GUEST:   Luke Kemp - Research affiliate at the Centre for the Study of Existential Risk at the University of Cambridg.  His first book - Goliath’s Curse: The History and Future of Societal Collapse - is due out in September