What led to the outbreak of first war between Greece and Persia?

The first war between Greece and Persia, known as the Greco-Persian War, was primarily sparked by the Ionian Revolt (499-494 BCE), where Greek city-states in Asia Minor rebelled against Persian rule. Athens and Eretria supported the revolt, angering the Persian King Darius I, who sought to punish them and expand his empire. This conflict escalated when Darius launched a military campaign against the Greek mainland, culminating in the famous Battle of Marathon in 490 BCE. The underlying tensions were also fueled by the growing power of the Greek city-states and their desire for autonomy.