About six months ago, I spent three days perched on the bunk of a lorry travelling from Abidjan, the coastal commercial capital of Ivory Coast, towards Ouagadougou, the capital of Burkina Faso in west Africa. Each day, we bumped along roads where there was more pothole than tarmac, carrying a load of carpets from a Lebanese businessman’s yard. Every few miles police lounged under trees, watching branches or lengths of string laid across the road, waiting to extract a bribe. With all the stops, we never got much faster than 15 miles per hour.

I took that trip to learn why Africa doesn’t trade with itself. But it taught me something about trade more generally and what lies behind the wealth of nations: if you