What group of outsiders had tyrannical control of the greek city-states in the sixth century BC

Answer

Greek Tyrants

Explanation:

In 404 BCE, following the defeat of the Athenian military forces in Sicily, there was an oligarchy of 'the Thirty Tyrants' in Athens which was a particularly brutal regime, noted for its summary executions. Megara and Thebes were other states which had an oligarchic system.