People were captured by Africans and enslaved. They were then taken by their African captors and sold at the coast for Manillas (copper and bronze armlets) that had been manufactured in Europe. The African kingdoms that ran the slave trade became very rich on the proceeds of selling Africans that they captured.
Africans traded gold, ivory, and other resources for goods such as firearms, textiles, and rum in the triangle trade. The main commodity that Africans were traded for in this trade route was slaves.
The short and simple answer is that they were not seen as humans, but as savages. The Africans that the pioneers found in their travels were usually simple hunters. They were capable of building only simple structures, hunting and gathering, and growing crops. Their social structures, if any, were unsophisticated compared to Europe and Asia. The pioneers saw this as a great opportunity for very cheap and abundant labor. They proceeded to ship the Africans back to America and made them do all of their hard labor.
Enslaved Africans looked upon the branding iron with horror, as it symbolized the dehumanizing process of being marked as property by their captors. This physical act reinforced their status as objects to be owned and traded, rather than as human beings with dignity and autonomy.
I the Triangular Trade the slaves didn't trade anything. Other african captured them during war and shipped them to the West Indies where they worked on plantations under harsh circumstances.
Slave traders traded goods such as guns, ammunition, textiles, beads, alcohol, and metalware in exchange for slaves in Africa. These goods were used to entice African leaders and traders to capture and sell slaves to European and American slave traders.