February 2017 - People in ancient Greece called everyone who didn't speak Greek a barbarian (barbaros). They said that people speaking other languages sounded like they were just going "bar, bar, bar, bar..." and that is why they called those people barbarians.
Don't let this fool you into thinking that these "barbarians" were all living in the Stone Age. The Greeks called Persians, Romans, Phoenicians, Scythians, Egyptians - all barbarians. Many of these people had more technology than the Greeks, better doctors, and better universities. "Barbarian" just meant that they did not speak Greek.
The Greeks believed that Greek people (or at least Greek men) were more rational than these barbarians. The Greeks thought that barbarians were ruled by their emotions instead of by reason. Also, barbarians had weird foreign customs: they drank beer instead of wine, they used marijuana, they wore long pants, and they let women fight in battle and ride horses.
That didn't stop the Greeks from working for foreigners, or having foreigners work for them though. In the Classical and Hellenistic periods, most of the Athenian police force was made up of enslaved Scythian. And throughout Greek history, many Greek men worked as mercenary soldiers or as artists in Egypt and Persia.
Ancient Greece , by Anne Pearson.
Greeks and Barbarians, by Thomas Harrison (2001).
Greeks, Romans and Barbarians: Spheres of Interaction, by Barry Cunliffe.