Final answer:
Leonidas took 300 Spartans plus several thousand other Greek allies to face the Persians at Thermopylae to delay them, even though they were overwhelmed eventually due to Greek betrayal.
Step-by-step explanation:
The Spartan king, Leonidas, was allowed to take a small force of 300 Spartans to the Battle of Thermopylae in 480 BCE, along with several thousand other Greek warriors, to face the massive Persian army led by Xerxes I. Although the Greek forces were heavily outnumbered, with estimates ranging up to 200,000 Persian soldiers and 1,200 ships, they used the narrow pass at Thermopylae to their strategic advantage.
Their goal was not to win but to delay the Persian forces, giving the Greeks time to prepare their defenses. The Spartans and their allies fought heroically and inflicted significant casualties on the Persians before being overwhelmed due to betrayal by a Greek that revealed a path to the Persians, allowing them to outflank the Greek position. The Spartans' sacrifice had a lasting impact, providing crucial time for the Greek city-states to unify and eventually secure victory in subsequent battles.