Stephen Sackur talks to president of South Sudan, Salva Kiir Mayardit, in Juba. The world's youngest nation, in December 2013 South Sudan became engulfed in a civil conflict which has claimed thousands of lives and prompted fears it could lead to genocide. A fragile ceasefire was agreed between the government of President Salva Kiir and his former deputy Riek Machar, who has led the rebel forces.