Nuer Language, Nuer people , Who are they? Or Who were they? Why they are targeted now by genocide?

http://en.wikipedia.org/wiki/Nuer_language

The Nuer language is a Nilo-Saharan language of the Western Nilotic group. It is spoken by the Nuer people of South Sudan and in western Ethiopia. Nuer is one of eastern and central Africa’s most widely spoken languages. The Nuer nation is one of the largest in South Sudan.

Nuer language has a Latin-based alphabet. There are also several dialects of Nuer, although all have one written standard. For example, while final /k/ is pronounced in the Jikany dialect, this sound is dropped in other dialects despite being indicated in Nuer orthography.

The Question is: South Sudan: Who kills whom and why??? There is some kind of tribal lethal  hostility.

http://wiki.answers.com/Q/How_many_tribes_are_in_south_Sudan?#slide=1