What role did the bantu have in the development of swahili culture?

The Bantu are an ancient group of people from Africa, whose origins are unclear. 
After the Portuguese were overthrown by the Omani Arabs in 1730, the Swahili were given some rights back, but the Omani Arab rule proved to be disastrous for the inland African tribes. 
Due to the need for cheap labor in the 18th century the Sultan of Oman, whose name was Sayyid Said, moved his seat of power, in 1840, to Zanzibar, near east Africa’s coast. His territory then expanded from northern Mozambique to southern Somalia. 
The people who were responsible for abducting slaves were agents of the Sultanate of Zanzibar and some African tribes.