Persistence studies are all the rage in economics – using clever maths to show that events in the distant past drive political or economic outcomes today. One well-known example argued that Britain’s superior growth to France as late as 1800 was shaped by… the collapse of the western Roman empire a millennium before. Here, the collapse saw the population de-urbanise, while in France they remained in Roman-era towns that lasted. So when Britain’s cities re-emerged they were in places better suited to growth in the run-up to the Industrial........