What led to the start of the Persian Wars? O The Athenians wanted to unify the city-states.
O The Spartans wanted to expand their territory.
O Xerxes I hoped to create an alliance with Sparta.
O Darius I wanted to punish Athens for supporting a revolt.

The Persian Wars began in 499 BCE, when Greeks in the Persian-controlled territory rose in the Ionian Revolt. Athens, and other Greek cities, sent aid, but were quickly forced to back down after defeat in 494 BCE. Subsequently, the Persians suffered many defeats at the hands of the Greeks, led by the Athenians.

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

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