Yes. The coastal African states (Such as Benin in the west and Zanzibar in the east) would capture inland tribes, and trade them to each other and Arab states for millennia. When Europeans came and wanted slaves to work on plantations in their new colonial empires, the coastal states started selling off slaves to them, too, and because of the great demand for slaves in these colonies, slavery in West Africa expanded. Once the demand for slaves died out in the Americas in the 19th century, the West African states returned to just trading amongst themselves, until they were annexed by European empires in the scramble for Africa, and with a new government with abolitionist laws, slavery in West Africa died out for the most part. A well known account showing this practice is the life of Abdulrahman Ibrahim Ibn Sori, a prince from the Imamate of Fouta Djallon who was captured by slave traders of an unknown enemy state in 1788, and sold off into slavery in Natchez, Mississippi. (Who later, thanks to President J.Q. Adams, managed to return to West Africa, although only to Liberia, he never made it back to Fouta Djallon.)

Hi OP, another good source is The Interesting Narrative of Olaudah Equiano. He was captured as a young boy and later bought his freedom; this book is his memoir and describes slavery in Africa in great detail, including how slaves were acquired.