When did Darius order the Greeks to obey him?

Darius I of Persia ordered the Greeks to obey him after his successful military campaigns in the region around 490 BCE. He dispatched messengers to various Greek city-states demanding their submission and the payment of tribute to Persia. This demand was met with resistance, particularly by Athens and Sparta, which ultimately contributed to the onset of the Greco-Persian Wars. The refusal of these city-states to comply set the stage for the famous Battle of Marathon in 490 BCE.