Wait, There's Two Sudans Now?

Five days ago, a new country was born. After years of conflict, the (very cleverly) named nation of South Sudan came into being. It isn't every day that a new country happens, of course, so it's worth taking a look at this particular case and see what the prospects are like for this new nation. The two big questions are, of course, why did this happen, and what are the new state's challenges? Also, what do you get a country for its birthday?