Sparta was a closed society, and losses of citizens in wars could not be replaced. These losses had been accumulating during the Peloponnese War in the 4th Century, and were compounded in the wars against the Theban confederation at Leuctra in 372 BCE, and Mantinea 362 BCE. As a consequence, as a rural community with a now low warrior strength, it simply didn't have the resources. Although Sparta joined with Arcadia and Achaea to block the pass at Thermopylae to prevent Philip of Macedon's push south, it subsequently decided it could no longer take the field with hostile neighbours Arcadia and Messenia (which Thebes had liberated from Spartan rule) threatening its territory. In consequence Sparta stayed at home as Philip overcame Greece.
To first destroy the Persian sea power which threatened the Greek city-states and so made them keep their armies at home defending their cities. With the sea threat gone, the cities could send out their armies to unite and take on the Persian army.
unite unify unite unify
the basilar artery.
C. American Colonies should unite
The Persians who was led by Xerxes .
They were very separated by the mountainous land, but in the Battle of Salamis Sparta and Athens united to take down the Persians.
The war against Persia. It united all of Greece, including Athens and Sparta.
To face a more powerful common enemy
They united 180 Greek city-states into several alliances, the first led by Sparta, the next led by Athens.
Sparta and Athens were natural allies who provided support to each other - Sparta leading the Dorian bloc of independent city-states, Athens the Ionian bloc, with both interested in maintaining peace. So when a Persian expedition was sent to subdue Athens in 490 BCE after its interference in the Ionian Revolt against Persia, Athens naturally asked Sparta for support (however Athens had defeated the Persians at Marathon by the time the Spartans arrived). When Persia sent a full scale invasion in 480 BCE, the southern Greek city-states united to repel it under the leadership of Sparta with Athens providing the largest naval component. They remained friends and allies until 460 BCE, when Athens sent an army to help the Spartans put down a revolt of its serf population. During this campaign they fell out and avoided each other. After the Persians agreed to peace the Athenians turned the Delian League into an empire of its own, became over-adventurous and clashed openly with the Peloponnesian League led by Sparta, resulting in the 27-year Peloponnesian War which Athens lost.
Originally? To unite Greeks against the threat of the Persians. After the defeat of the Persians? To execute and maintain Athenian hegemony in the Aegean. Or to put the second point in another way, to give Athens the money to keep its fleet in place to enforce the annual collection of funds from the members, and spend the rest of the tribute on improving its own city and keep half its people on the public payroll.
Athens and Sparta were independent City-States and therefore were not especially close. However, the Greeks did unite to repel foreign invasions. One of the reasons that Sparta and Athens went to war (The peloponnesian war), was because after the city of Athens was destroyed by Persian invaders, the Athenians stole large sums of money from the Delian League to rebuild their city (and also some of their most famous modern wonders, such as the Parthenon), which was a national treasury set up by the primary City-States of Greece. This action enraged the Spartans in particular, and caused the war.
Self defence.
Most rational people think they fought them.
Sparta was a closed society, and losses of citizens in wars could not be replaced. These losses had been accumulating during the Peloponnese War in the 4th Century, and were compounded in the wars against the Theban confederation at Leuctra in 372 BCE, and Mantinea 362 BCE. As a consequence, as a rural community with a now low warrior strength, it simply didn't have the resources. Although Sparta joined with Arcadia and Achaea to block the pass at Thermopylae to prevent Philip of Macedon's push south, it subsequently decided it could no longer take the field with hostile neighbours Arcadia and Messenia (which Thebes had liberated from Spartan rule) threatening its territory. In consequence Sparta stayed at home as Philip overcame Greece.
The Persians had to send half their army home as, with their sea supply line unprotected by their defeated fleet, they could not feed them in the oncoming winter. This left the way open for the Greek cities to unite and defeat them in the next spring.