OBI ANYADIKE THE scale of Boko Haram's insurgency in northeastern Nigeria has long been clear. But it took the abduction last month of more than 340 schoolboys for many people – even within Nigeria – to appreciate just how bad the insecurity has become in the country’s neglected northwest. The abductors pulled up on motorbikes at the all-boys secondary school in Kankara, in Katsina State, spent an hour rounding up the students who didn’t manage to bolt, and then marched them into Rugu forest in neighbouring Zamfara State. In a video message, the kidnappers said they were Boko Haram, a claim endorsed by…