The SSLM was formed in the context of widespread factional fighting among the Western Nuer ethnic group of Unity, South Sudan, who had signed a peace treaty with the government on 21 April 1997.

The pro-government SSDF militia, comprising a large number of Nuer, had divided into warring factions led by Riek Machar and Paulino Matip.

As Riek was being defeated, opposing government-aligned militias attacked civilians around the oilfields in South Sudan, causing a stream of Nuer refugees to flee towards SPLA-controlled Bahr al-Ghazal for protection.

Groups of Western Nuer and Dinka from Tonj, Rumbek and Yirol took part, leading to a peace agreement in March 1999 to end the ethnic fighting.

[10] During the South Sudanese Civil War, former SSLA troops who had been assimilated into the SPLA moved to expel rebel factions loyal to Riek Machar from Bentiu.