Without guns, he would have difficulty in protecting himself and his people.

Any ruler or people who could not provide adequate self-defense could be captured and sold into slavery.

Once begun, the Africans found themselves enmeshed in a vicious system from which there seemed to be no escape.

The only possibility for escape would have been the development of some kind of African coalition, but each petty ruler as too concerned with his own power to be able to contemplate federated activity.

European greed fed African greed, and vice a versa.
In the beginning, African slaves were carried back to Portugal and other parts of Europe to be used as exotic domestic servants.