The race to lead sub-Saharan Africa's largest country kicks off this week with presidential candidates registering for Congo's November election. The upcoming vote threatens to spark even more violence in this nation already wracked by back-to-back civil wars, and which is still haunted by a myriad of armed groups. Incumbent Joseph Kabila, who first took power after his father's assassination more than a decade ago, had appeared all but certain of victory until the opposition announced some surprising challengers. But those opposition figures will have to unite if they have any hope of ousting Kabila. Constitution changes since the last vote in 2006 have done away with a two-round voting system and replaced it with a single ballot.