In 499 BCE, the tyrant of Miletus, Aristagoras, launched an attempt to conquer Naxos to bolster his position. But the mission failed, and Aristagoras feared he would be removed as tyrant. So he incited the Ionians to rebel against the Achaemenid Empire. This started a chain of events that led to the Greco-Persian Wars.

Let us suppose that the mission had been a success and so there was no revolt. What would change?
 
Ionia was ripe for rebellion anyway, as they were not really happy with their tyrants, and the push for Darius to expand into Thrace and Scythia caused a removal of currency, which harmed the Ionian trade centers, and the impressment of Ionian sailors and trading ships into the fleet allowed competitors to seize lucrative trading opportunities, as just a few of many reasons why the Ionians revolted. Aristagoras simply built upon already-present discontent and turned it into rebellion. Though, without Aristagoras leading the revolt, it might be less successful, and the Athenians and Eretrians might not burn Sardis, which would impact the subsequent Greco-Persian wars. Alternatively, the Naxians might join the Ionians in rebellion.
 
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