They joined the spartans and won the war
The battle of Thermopylae.
The defence of the pass at Thermopylae by 7,000 Greek soldiers, including the Spartans, lasted three days.
The purpose of the Thermopylae delay was to provoke a sea battle in the nearby strait of Artemesion, in the hope of destroying the Persian fleet. The Persian fleet won, and the Greeks had to withdraw to try again at Salamis, which they did win. The Thermopylae delay had no effect on the outcome of the war.
There was no 'Thrmopylai War'. there was a short engageent at Thermopylai as part of the Persian pust into southern Greece.
The Spartans were involved in the Persian Wars, particularly the battle of Thermopylae (where 300 Spartans famously held off the Persians), the Peloponnesian War (against the Athenians), and other minor skirmishes with neighboring city states, which usually ended with the Spartans conquering the other city state.
The movie 300 is based on the Battle of Thermopylae, an actual battle that took place in ancient Greece. The war was between The Greeks and the Persians. There really were 300 Spartans, but there was also about 10,000 other Greek soldiers, so the Spartans were not alone. The Greeks lost the Battle of Thermopylae, but the Spartans fought bravely and more valiantly than the rest with their superior phalanx military strategy.
The slowing of the Persian advance at Thermopylae by a force from Greek cities, including Sparta, was to force a sea battle ,but the Greek lost at sea, and the delaying force at Thermopylae was withdrawn. The Greeks won their sea battle at Salamis later on, so Thermopylae had no effect on the outcome of the war. It did, however, become a symbol of staunch resistance.
The Battle of Thermopylae, fought in 480 BCE during the Greco-Persian Wars, involved an alliance of Greek city-states led by King Leonidas I of Sparta against the invading Persian forces commanded by King Xerxes I. The Greek contingent comprised around 7,000 soldiers, with a significant force of 300 Spartans who famously stood their ground at the narrow pass of Thermopylae. The battle is renowned for the Spartans' valor and sacrifice, ultimately culminating in their defeat but serving as a symbol of resistance against tyranny.
so they would have the advantage in war.
Exactly that, to slow them down. Also, the oracles said that Sparta couldn't go to war. It was Spartan tradition that if the king was killed, then they had to go to war. The king (Leonidas) basically went to Thermopylae to get himself killed. On a different note, 300 men taking out half the Persian army was great for Morale.
so they would have the advantage in war.