Final answer:
The slave trade in West Africa existed before European contact but was expanded and intensified by the Portuguese demand for slaves to serve on sugar plantations, marking the beginnings of the Trans-Atlantic slave trade.
Step-by-step explanation:
According to the excerpt by David Wheat on the Portuguese establishment of trade networks and their interaction with African societies, the slave trade in West Africa existed prior to contact with Europeans but was significantly stimulated by European demand for chattel slaves. The Portuguese were not the creators of the slave trade in Africa, as slavery existed among African states, but they elevated this trade to new heights by transporting enslaved people to work on their sugar plantations on various Atlantic islands and later into European nations.
The Trans-Atlantic slave trade was thus fueled by European demand for labor-intensive crops like sugar, cotton, and rice, leading to the development of these commodities on plantations which heavily utilized enslaved African labor. It's notable that while the Portuguese initially engaged in trade and diplomatic relations, their economic pursuits eventually led to the establishment of several colonies peopled by Iberians and Luso-Africans, signaling the transition of trading posts into full-fledged colonial enterprises.