Why was king Darius angry at the Athenian?

King Darius of Persia was angry at the Athenians primarily because they supported the Ionian Revolt against Persian rule. The Athenians sent ships and troops to aid the Ionian cities, which defied Persian authority and threatened Darius’s control over the region. In retaliation, Darius sought to punish Athens, leading to the famous Battle of Marathon in 490 BCE. This conflict marked a significant moment in the struggle between Persia and the Greek city-states.