THE WORLD’S newest country, South Sudan, celebrates its first birthday on Monday after decades of civil war between the south and north. But the optimism that prevailed a year ago has largely faded. South Sudanese leaders are continuing to act like the ragtag rebels they used to be rather than a modern government. The time for blaming the regime in Khartoum for all of South Sudan’s problems is over. If the US investment in Sudan is to pay off, and the Sudanese people avoid a renewal of the war that resulted in 2 million deaths, South Sudan must grow up quickly.

The United States, which has helped midwife the fledgling nation, should hold the leaders of South Sudan accountable for the reckless decisions they have made. Among the worst was their invasion of the disputed oil-producing region of Heglig, which is widely seen as belonging to the north. That aggressive action has brought the north and the south back to the brink of war. Even more disastrously, South Sudan has shut down oil production in its territory over a dispute with the north on a series of outstanding issues.

The spiteful move is hurting South Sudan itself far more than the north. The fledgling government is starving itself of oil, its only source of revenue. A leaked World Bank report predicts that South Sudan will run out of its fiscal reserves as early as the end of this month. The poverty rate is expected to rise from 50 percent of the population to 80 percent unless the oil is turned back on. As if the situation were not bad enough, South Sudanese president Salva Kiir recently accused 75 government officials of plundering some $4 billion in public funds.

All this comes at time when drought and ethnic conflict have uprooted hundreds of thousands. In the past, South Sudan’s leaders have always been able to count on foreign aid to keep its population alive. During the war, the United Nations and a host of nongovernmental aid agencies flew in planeloads of food and medical supplies to Juba. But now, South Sudan’s destiny is in the hands of its people. The suppliers of aid should use their leverage to push for greater self-sufficiency from South Sudan, along with better decision-making. The leaders of the south must learn that true independence means developing a healthy economy and slowly growing free of foreign aid.