This marked the beginning of the first war in southern Sudan.
In southern Sudan each side will contribute 12,000 soldiers to the joint force.
Prior to 1975 it had also been spoken in southern Sudan.
Far less is known about the history of southern Sudan.
In 1964 all foreign missionaries were made to leave southern Sudan because of the civil war.
It was established by journalists from southern Sudan in 2000.
Because of the civil war in southern Sudan from 1983, more recent research on this issue has been restricted.
A return to southern Sudan would be dangerous, if not fatal.
A war against the people of southern Sudan has been going on there for decades.
Aid workers have been leaving the southern Sudan in the last month.