2. The Kingdom of Dahomey is not modern-day Benin. In fact, Benin was deliberately renamed from Dahomey (the French had used that name for it as a colony).
3. It's probably not productive to single out any one African people in the slave trade. What seems to be the truth is that the slave trade was a vicious cycle driven by demand from outside the continent: great world powers would trade military technology for slaves, meaning that most tribe/states in Africa were essentially locked in an arms race to avoid themselves being enslaved. There was slavery in Africa (like basically everywhere else in the world at one point or another) before the Trans-Atlantic Slave Trade, but the Trans-Atlantic Trade was a sui generis world-historical event, at a whole new scale (by percentage perhaps the largest forced movement in human history) and it wasn't caused by Benin.