On average about how many slaves per year were brought to the americas in the 1600s

For the intention of using them in sugar production.
The first slaves were brought to Jamestown in 1619.
Usually, during this time period, indentured servants were the ones coming to American because their passage fees were paid by wealthy English merchant who "bought" a few years of their labor. It was like being their servant for a certain number of years in order to go to America and eventually be free and gain land.
However, when settlers came to the United States, colonists began to view indentured servants as too costly, and in 1619, Dutch traders brought the first African slaves to Jamestown, who nonetheless were generally treated as indentured servants.

Because broadest terms allows the law flexibility depending on changing society and circumstances.