I am currently reading through “American Slavery: A Very Short Introduction” and in the opening chapter, where it covers the history of African slavery under Portugal and Europe, it states:
“As the Portuguese and other Europeans expanded their desire for slaves, they entered into arrangements with African rulers who allowed African traders to go inland to capture people whom they marched to the coast and traded with waiting Europeans ... Some African rulers negotiated with Europeans and imposed duties or taxes on the trade, made demands regarding the goods they wanted as payment, and benefitted from systems of gift-giving.”
The chapter then explains that the African communities at the time did not consider themselves united as a single group based on being from the sameness country or due to skin colour but that “their identities instead derived from being members of a specific village or an ethnic group. Therefore, they did not sustain a sense of unity with, or loyalty to, captives from other groups. In fact, people were generally captured in wars with other groups that increased in frequency as African traders obtained weapons from Europeans.”
Do we know which particular rulers or societies engaged in this part of the slave trade? Was one tribe more active in enslaving, or in being enslaved, than the others and did this increase or decrease as the centuries went by, including leading up to the time period of the American Revolution and the later periods of abolition?
EDIT: I screwed up royally by using the word “tribes” instead of societies, it just goes to show my ignorance and inexperience with the subject and I deeply apologise for the use of the term, I have amended the section above to include the correct word. Unfortunately I am unable to edit the title without deleting the post and reposting the question as a new one.
Africanists avoid using the term tribe. So, for the rest of this answer I will instead refer to them as particular societies/communities, or as kingdoms or chiefdoms, as is appropriate.
The short answer is, we have a pretty good idea of numbers and regions where enslaved Africans embarked from. Historical records of enslaved peoples names also give clues to what community that person was from. The Trans-Atlantic Slave Trad Database is a good resource for this. It contains maps depicting ports and regions with general numbers of enslaved people shipped out. It also contains a database of ship crossings, including date, port of departure and of arrival, and number of people carried. Also, it has a database of named African individuals, their port of departure, and sometimes notes on their ethnic origin.
Also, there is a grate deal of secondary literature on the topic as well. Gwendolyn Midlo Halls Slavery and African Ethnicities in the New World: restoring the links deals heavily in identifying when large numbers of Africans from one community arrived in the same region in the new world. e.g. lots of Coromanti arriving in Jamaica, lots of Yoruba in Bahia, Brazil, lots of Kongo in South Carolina. She also relies heavily on ships records, advertisements and bills of sale that detail ethnicity, as well as fairly rare slave biographies where individuals say for themselves what their ethnicity was.
There's also work by John Thornton and Linda Heywood about Central African diasporas in the Americas. e.g. Kongolese, Mbunda, Ovimbunda, Vili, Teke, Imbangala who arrived in Brazil, the carribean and North America. I'm thinking particularly of Thornton's Africa and Africans, Heywoods Central Africans and Cultural Transformations in the Diaspora and Thornton and Heywoods chapter in Soundings in Atlantic History edited by Bayly.
Also, there are compendiums of primary source documents like Africa and the West: A documentary history which contain individual letters by European ship officers, African monarchs, emancipated slaves, etc, which have details like what society/kingdom and what monarch was doing the raiding, and where the port they were emarking from.
than the others and did this increase or decrease as the centuries went by, including leading up to the time period of the American Revolution and the later periods of abolition?
Yes, as you speculate, the slave trade was not stable, but experienced gradual growth from 1500-1700 (approximately 340,000 embarked from 1500-1600, 1.8 million embarked from 1600-1700). Massive growth from 1700-1800 (circa 6.5 million ) and a decline from 1800-1900 (circa 4 million) with the most precipitous decline from 1830-1860. All numbers from Transformations in Slavery by paul lovejoy.
And as you correctly assume, players that were important early on like Allada in 1600 or Loango in 1700 were superseded later on by more powerful competitors like Dahomey, Ashanti empire, Oyo, Kongo. And sometimes societies that had not been part of the slave trade became engaged in slave trading later on, like the Ovimbundu from 1750s-1880s.