U.S. and European oil and gas majors are back to doing business in Libya, a decade after pulling out as civil war engulfed one of the top oil producers and the biggest oil resource holder in Africa. Amid a relatively calm security situation this year, Libya launched its first bid round for oil and gas exploration in 18 years. The previous such bid round was held in 2007, four years before the toppling of Muammar Ghaddafi in 2011, which led to a protracted civil war in the country with various factions and tribal interests vying for control…