U.S. and African officials seeking to mediate an end to South Sudan's bloodshed are, in effect, trying to repair rifts in the very liberation movement that they supported for years. The conflict, which pits powerful tribes against each other, is also a political struggle that threatens to shatter one of the continent's most storied groups of freedom fighters.

After South Sudan won independence from Sudan in 2011, U.S. diplomats and analysts expected that lingering animosities over oil revenue, disputed boundaries and security would be the biggest challenges facing the world's newest nation.

Instead, the leaders whom Washington nurtured threaten to unravel one of America's most significant policy successes in sub-Saharan Africa in this century.