The West African empires of this period peaked in power in the late 18th century, paralleling the peak of the Atlantic slave trade. These empires implemented a culture of permanent warfare in order to generate the required numbers of captives required to satisfy the demand for slaves by the European colonies. With the gradual abolition of slavery in the European colonial empires during the 19th century, slave trade again became less lucrative and the West African empires entered a period of decline, and mostly collapsed by the end of the 19th century.[9]