Passage: A mercantile class arose in the first half of the 7th century BC, shown by the introduction of coinage in about 680 BC. This seems to have introduced tension to many city-states. The aristocratic regimes which generally governed the poleis were threatened by the new-found wealth of merchants, who in turn desired political power. From 650 BC onwards, the aristocracies had to fight not to be overthrown and replaced by populist tyrants. This word derives from the non-pejorative Greek τύραννος tyrannos, meaning 'illegitimate ruler', and was applicable to both good and bad leaders alike.A growing population and a shortage of land also seem to have created internal strife between the poor and the rich in many city-states. In Sparta, the Messenian Wars resulted in the conquest of Messenia and enserfment of the Messenians, beginning in the latter half of the 8th century BC, an act without precedent in ancient Greece. This practice allowed a social revolution to occur. The subjugated population, thenceforth known as helots, farmed and labored for Sparta, whilst every Spartan male citizen became a soldier of the Spartan Army in a permanently militarized state. Even the elite were obliged to live and train as soldiers; this commonality between rich and poor citizens served to defuse the social conflict. These reforms, attributed to Lycurgus of Sparta, were probably complete by 650 BC.

Question: Who threatened to replace the aristocracies?
populist tyrants