What is a reason south sudan separated from sudan and became independent in 2011

Because people who are non-Arab, Christian, and animist, have long felt oppressed by their neighbors in the Arab and Muslim North.
Hope this helped.

The decision to secede can be traced to the northern Sudanese government's consistent policy of marginalization of the southern part of the country since Sudan became independent in 1956. The people of the South, who are non-Arab, Christian, and animist, have long felt oppressed by their neighbors in the Arab and Muslim North.