The statement "In the ancient world, slaves were often war captives or debtors" accurately reflects a key difference between slavery in the ancient world and slavery in the Americas. In many ancient societies, slavery was often the result of warfare, piracy, or the inability to pay debts, and it was not uncommon for slaves to eventually gain their freedom. In contrast, slavery in the Americas, particularly during the transatlantic slave trade, involved the forced transportation of millions of Africans to work on plantations under brutal conditions, with a racial component that marked it as a distinct system of chattel slavery.
While the other statements touch on aspects of slavery, they do not capture the fundamental difference as effectively as the one regarding the origins of slavery in ancient societies.