 With the exception of Portuguese-controlled Angola, coastal African leaders "generally controlled access to their coasts, and were able to prevent direct enslavement of their subjects and citizens".Thus, as African scholar John Thornton argues, African leaders who allowed the continuation of the slave trade likely derived an economic benefit from selling their subjects to Europeans.The Kingdom of Benin, for instance, participated in the African slave trade, at will, from 1715 to 1735, surprising Dutch traders, who had not expected to buy slaves in Benin.