A new civil war that broke out in December 2013, has contributed to the economy's fall. Oilfields all along South Sudan have been threatened by rebels and the oil production right now is even worse than when they had just independenced
In 2012 the South Sudanese government shut down the oil production due to the row with the northen part of Sudan and to the fact they did not have the resources Sudan had to exploit the oil (refineries)
Debts: From 2012 to 2013, their economy didn't grow, not even after have restored relations with Sudan, because all that time they were just paying what they'd previously borrowed
Corruption: Money is not equally distributed, politicians and army are mainly benefited