AP Photo

The Obama administration, elsewhere challenged by Iranian nuclear ambitions and North Korean brinkmanship, is on the verge of a major diplomatic achievement in Sudan. Barring technical failures that delay the vote, or unexpected violence, South Sudan will approve an independence referendum on Jan. 9. Six months later, a new flag will rise, a new anthem will be played. It is a rare, risky, deeply American enterprise: midwifing the birth of a new nation.