The rapid deterioration of Libya’s oil-dependent economy is threatening the objectives of the country’s new Western-backed government and budding efforts to confront the Islamic State in North Africa, political and security analysts say. Within hours of arriving in Tripoli two weeks ago, the government made controlling the nation’s oil a priority. It persuaded a powerful militia to hand over three oil terminals, and the national oil company gave its support. But the road to securing Africa’s largest reserves is riddled with even greater obstacles, and bringing the battered industry back to its full potential promises to be a colossal mission....