Prior to the brits, there was trade along the East African coast; past the Middle East, all the way to India. The main language along the coast became a fusion of Arabic, Indian and Bantu languages. Swahili adopts Arabic arithmetic & language structures e.g 15 is said as ten and five, 7 is Saba. A minister is wazir etc.
Many Old Bantu words such as mti for tree are in Swahili. similarly sounding words are used in languages from west Africa to South Africa (muti, miti).
From India, we have Pilau, chapati, dhania...
http://www.rahmahmuslimhomeschool.co.uk/index/wp-content/upl...
http://www.languagesgulper.com/eng/Bantu.html
https://en.m.wiktionary.org/wiki/Category:Swahili_terms_deri...