Somali Bantus did not come to Somalia as part of the Bantu Expansion. They were brought by the Omanis as slaves and bought by Somali masters as part of a plantation system mostly along the Webi Shebelli. Those in the Jubba/Kismayo area descend mostly from slaves who escaped the Shebelli area and became independent in the forested/tsetse-infected area of the Gosha.
http://en.wikipedia.org/wiki/Somali_Bantu
"Between 2500–3000 years ago, speakers of the original proto-Bantu language group began a millennia-long series of migrations eastward from their original homeland in the general Nigeria and Cameroon area of West Africa.[7] This Bantu expansion first introduced Bantu peoples to central, southern and southeastern Africa, regions where they had previously been absent from.[8][9]
The Bantus inhabiting Somalia are descended from Bantu groups that had settled in Southeast Africa after the initial expansion from Nigeria/Cameroon, and whose members were later captured and sold into the Arab slave trade.[8]
The Indian Ocean slave trade was multi-directional and changed over time. To meet the demand for menial labor, black Africans from southeastern Africa captured by Arab slave traders were sold in cumulatively large numbers over the centuries to customers in Egypt, Arabia, the Persian Gulf, India, the Far East, the Indian Ocean islands, Ethiopia and Somalia.[2][3]
From 1800 to 1890, between 25,000–50,000 black African slaves are thought to have been sold from the slave market of Zanzibar to the Somali coast.[10] Most of the slaves were from the Majindo, Makua, Nyasa, Yao, Zalama, Zaramo and Zigua ethnic groups of Tanzania, Mozambique and Malawi. Collectively, these Bantu groups are known as Mushunguli, which is a term taken from Mzigula, the Zigua tribe's word for "people" (the word holds multiple implied meanings including "worker", "foreigner", and "slave").[2]
19th and 20th centuries
Bantu slaves were made to work in plantations owned by Somalis along the Shebelle and Jubba rivers, harvesting lucrative cash crops such as grain and cotton.[11]
In the 1840s, the first fugitive slaves from the Shebelle valley began to settle in the Jubba valley. By the early 1900s, an estimated 35,000 former Bantu slaves settled there.
The Italian colonial administration abolished slavery in Somalia at the turn of the 20th century. Some Bantu groups, however, remained enslaved well until the 1930s, and continued to be despised and discriminated against by large parts of Somali society.[12]
The Bantus were also conscripted to forced labor on Italian-owned plantations since the Somalis themselves were averse to what they deemed menial labor,[13] and because the Italians viewed the Somalis as racially superior to the Bantu.[14]
“ While upholding the perception of Somalis as distinct from and superior to the European construct of "black Africans", both British and Italian colonial administrators placed the Jubba valley population in the latter category. Colonial discourse described the Jubba valley as occupied by a distinct group of inferior races, collectively identified as the WaGosha by the British and the WaGoscia by the Italians. Colonial authorities administratively distinguished the Gosha as an inferior social category, delineating a separate Gosha political district called Goshaland, and proposing a "native reserve" for the Gosha.[14] ”
When I arrived in 1966, Jilib was the Italian administrative center for the LowerJubba, and the mayor of Jilib was Muhammed Sheikh Suleiman, the Gosha headman. This changed after the Kacaan, when Jilib and the Gosha were removed from the administrative picture.