Two comments - this bit of history, such as it is, happened long after the West African slave trade had been suppressed (1890).
Dahomey as a state entity did participate in the trade extensively, and its reasonable to say that it owed its growth and power to it, but in an earler time, the 17th-18th centuries.
The French took the region with very low casualties. The battles were the usual colonial massacres of ill-armed and ill-trained natives. Note: we tend to over-emphasize those few cases where the colonizers were defeated, but these were the exceptions.
Islandlwana.