The current fighting is not just about oil, however. Christian churches have long been interested in the region, and some of the more evangelical ones see South Sudan as a bulwark against Islam. Most South Sudanese follow traditional religions, but there is a sizable Christian minority.
The Congressional Black Caucus is involved because black southerners have been much oppressed by the Arab-dominated north. And the terrible civilian toll in the two civil wars has drawn support from human rights advocates.
Starting with the Trans Sahel Initiative in 2002, the U.S. has steady built up its military forces on the continent.
The U.S. now has troops in some 35 countries in Africa. Washington has deployed somewhere between 12,000 and 15,000 troops in Djibouti on the horn of Africa and at least 100 Special Forces in Uganda and Niger. It is training Kenyans to fight the Shabab in Somalia, Ugandans to track the Lord's Resistance Army in the Democratic Republic of the Congo, and it is building a drone base in Niger.
In 2006, the Bush administration created Africom, the first U.S. military command organization for the continent, whose coming out party was the overthrow of Libya's Mummer Khadafy in 2011. As the African Union predicted, Khadafy's fall spread a tidal wave of arms into the region that fueled civil wars in Mali, Niger and Central Africa.