Final answer:
Karen Tranberg Hansen conducted research on the secondhand clothing trade in sub-Saharan Africa. The historical context provided in the question involves the trade of enslaved individuals by West African kingdoms to European traders, influencing the socio-political landscape of the continent.
Step-by-step explanation:
Karen Tranberg Hansen studied the secondhand clothing trade in sub-Saharan Africa. However, the provided text does not directly relate to her work but rather provides historical context on the trade of enslaved people which had been a significant aspect of African commerce since antiquity. Within this trade network, West African kingdoms played a central role, as they were involved in capturing, transporting, and selling men, women, and children to European slave traders. With the arrival of European powers, the demand and scope for enslaved individuals grew, leading to increased militarization of African states and a shift in trade practices. Cities like Timbuktu, Gao, and Djenné were significant trade hubs that not only dealt in goods such as gold and salt but also participated in the slave trade. The destruction of the Songhai Empire and the increased European involvement transformed the socio-political landscape of West Africa and the slave trade therein.