The correct answer is A. The slave traders captured them in war.
Step-by-step explanation:
Most slaves that were taken from West Africa to America as part of the Atlantic Slave Trade that took place from the XVI to the XIX century were captured by slave traders during war or bought by slave trades to African tribes that had slave prisoners. This means most of Africans that were taken to America as slaves were war prisoners before being sailed through the Atlantic. During this centuries it is estimated around 12 million Africans were captured and taken through the Atlantic although some of them died in the trip. Considering this, it can be concluded slave trades obtain slaves by capturing them in war.