What did Africans primarily come to the Americas as?

Assuming that you are asking about the time between the
European "discovery" of the Americas and the late 1800s, Africans primarily came to the
Americas as slaves.

Beginning in the early 1500s, Europeans
were bringing Africans to the New World as slaves.  As can be seen in the link below,
there were 10,000 African slaves being brought just to the Caribbean (not counting
Mexico or mainland South America) each year.  According to some historians, the total
number of slaves brought to the Americas was around 11 million by the time the slave
trade ended.

During that time, then, most Africans who came
to the Americas came as slaves.