Foreign powers hope a nascent peace deal in Libya will be a prelude to concerted action against IS. But the omens for success do not look good.

As Libya approaches five years since the uprising began that culminated in the removal of long-time leader Mu’ammar al Qadhafi in 2011, there has been no let-up in the chaos that has succeeded his 41-year rule. Oil production is down to around a quarter of its 1.6mn b/d pre-conflict capacity. Fighting continues across the country between...