The most powerful Greek polis.
They established an Oligarchy, which means a small group of leaders rule. They made all the decisions. Another great achievement of the Spartans was how much land they conquered. Most city - states only controlled anywhere from 50 to 500 square miles of land. Sparta had over 4000. The largest area they conquered was Messenia. They enslaved the people and forced them to work. These Messenians rebelled and almost defeated the Spartans. This led to the decision to devote Sparta into creating the strongest army ever.
Spartans served in the military until they were 30. Then they were military reserves until age 60. Spartan girls were not only trained to be able to support the house, but also sports and athletics to be able to produce better soldiers. This is why Sparta had the strongest military in Greece.
The Persian Wars
Now, the Greeks only chance was excellent strategy. In the battle of Marathon, The Greeks defeated more than twice as many Persians. The marathon race was established in this battle. Then later, at the Battle of Thermopylae, the Greeks sent a small diversion force to defeat the Persian fleet off the coast of Salamis. This allowed the Greeks to win the war.
The Peloponnesian Wars
Later, Athens went to attack an ally of Sparta. Its army was surprised and defeated by the Spartans. This greatly weakened Athens. Nine years later, Sparta won the war against Athens, and the Delian League collapsed. Sadly, this weakened all of Greece.
Why is Sparta more powerful than Athens?
The Spartans trained their whole life to be in battle, while the Athenians lived daily lives and participated in government. Why would the Spartans NOT be able to defeat the Athenians? The only thing that Athens beats Sparta in is government. Democracy is much more efficient than an Oligarchy.