The reason why Athens and Sparta joined forces and fought for 20 years to protect Greece was because the Persians invaded the Greek Homeland.
Why did the Athenians and the Spartans forge an alliance?
The Persians had conquered a significant part of the known world and wanted to add Greece to their domain.
They therefore invaded the Greek homeland under various emperors and the Athenians and the Spartans responded by allying together and fighting the Persians.
Find out more on the Greeks and the Persians at https://brainly.com/question/1528624.
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