What made Sparta unique in Ancient Greece?

Not a lot. Mainly the heavy militaristic social order and of course the harshly autocratic monarchy. I'd say the biggest differences in Spartan society from the rest of Greece was: 1. read more

But I wouldn't really go as far as to say that Sparta was "unique". You'd probably be able to find several other Greek poleis like it. It was more that it was different from the Athenian lead Delian League and the Ionian Greeks in the East. read more

Sparta thus came to control some 8,500 km² of territory making the polis or city-state the largest in Greece and a major player in Greek politics. The conquered peoples of Messenia and Laconia, known as perioikoi, had no political rights in Sparta and were often made to serve with the Spartan army. read more

Sparta was unique in ancient Greece for its social system and constitution, which configured their entire society to maximize military proficiency at all costs, and completely focused on military training and excellence. read more