True enough, slavery has been around a long time and in many forms. However, chattel slavery in the Americas is different because it was lifelong and heriditary.

In various other times and places one could become a slave as a prisoner of war, or due to crime, or the settlement of debts, etc. These slaves would serve for a time, even for the remainder of their lives. Yet they were still regarded as human. Their children were not born into slavery. They were not relegated to semi-human status in perpetuity. Please consider these things before you interject "but everyone was slaves at one time or another" into conversations like this one.