When did slave trading start?

Answer 1

Since the dawn of man there have been slaves. Slaves were ( still are) taken in war and raids. Pirates often sold slaves through out the world to Greek, Roman, and other civilizations. Slavery built many of the ancient cities and temples. Slavery still goes on today and is not something that has disappeared, but has only gone more or less underground. Children in many third world countries are sold into slavery for sex and war. Even in the United States slavery still exists. Often illegal immigrants are kept as slaves because they still owe for the passage to the United States. Young women are kept as sex slaves by pimps and sold back and forth. This is not something that is gone or in the past.

Answer 2

Probably with the earliest civilizations thousands of years ago (if not earlier). But we can never know as there are no written records from those times. But all civilizations that have had written records (until the last couple of hundred years) have had slaves and traded slaves.