Unresolved disputes between the north and south, particularly over the new border, have also raised the possibility of renewed conflict.
Fears of fresh violence resurfaced after recent fighting in two border areas, Abyei and South Kordofan, where some 170,000 people have been forced from their homes.
But separate deals - and the withdrawal of rival forces from the border - have calmed tensions.
The UN Security Council has passed a resolution approving a 7,000-strong peacekeeping force for South Sudan - but this is basically a rebranding of the force that was already in Sudan, mostly in the south.
Our correspondent says keeping both the north and the south stable long after the celebratory parties have ended will be a challenge.
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