Complex sentence: The NSCC most widely reported success was the negotiation of an end to inter-ethnic fighting among Nuer in 1999 that led to the creation of the South Sudan Liberation Movement, which declared itself neutral in the conflict.
Split into simpler sentences: The NSCC most widely reported success was the negotiation of an end to inter-ethnic fighting among Nuer in 1999. The Wunlit negotiations led to the creation of the South Sudan Liberation Movement, which declared itself neutral in the conflict.