UN barges in Sudan attacked John Boonstra June 15, 2009 Another place where providing food aid is not easy: At least 40 south Sudanese soldiers and civilians were killed when tribal fighters ambushed boats carrying U.N. food aid, the latest in a string of ethnic attacks threatening a fragile peace deal, officials said on Sunday. Members of the Jikany Nuer group opened fire on 27 boats loaded with emergency rations destined for an area controlled by the rival Lou Nuer tribe on Friday, the U.N. World Food Programme said. It's long been a rather obvious point among Sudan watchers that the country's fate is tied more along the North-South axis than to the more prominent (and no, not unrelated) Darfur issue. A referendum on southern independence is scheduled for 2011, and there seems little chance, at least in the current climate, that South Sudanese won't vote for separation. If another war is then in the offing, a strategy of the government is Khartoum would almost certainly be to arm certain tribes in the south, in an attempt to sow internal strife among their adversaries. It's not a good sign, then, that the Sudanese government appears to have armed the group that carried out the raid on Sunday.