Final answer:
Europeans saw Africans as inferior and based their justification for enslavement on racism and the belief of African inferiority. Africans participated in the trade for economic gain and desired goods from Europeans.
Step-by-step explanation:
The Africans and Europeans justified trading slaves through various means. Europeans viewed Africans as primitive and heathen people, which they used as a basis for their superiority and the justification for enslaving them. In 1452, the Pope even granted Portugal the right to enslave non-Christians in West Africa.
On the other hand, Africans participated in the slave trade to gain wealth, power, and goods from European traders. They captured and enslaved other Africans to sell to Europeans, who provided firearms, textiles, alcohol, and other desired goods in exchange. The trade also caused conflicts and wars within Africa.
Overall, the justifications were based on racism, economic motives, and power dynamics between Africans and Europeans.