How did the Ionian Greek cities lead to war with the Persians

The Greek cities of Asia Minor and the Islands (nearly 200 of them) had been incorporated in the Persian Empire, but revolted in 499 BCE. This had been put down decisively by 494 BCE, but in the course of it the mainland Greece cities of Athens and Eretria had come to the aid of their daughter-cities there, and overdid it by burning down the Persian provincial capital Sardis.

The Persians, having suppressed the revolt in Asia Minor, set about stopping a repitition of this external aid and encoouragement, and mounted an amphibious expedition, planing to export the hostile parts of the population of the two cities and impose governments friendly to Persia.

Eretria was reduced and a puppet government installed. The earlier-expelled tyrant of Athens was brought along to re-establish friendly-to-Persia control of that city, but the expedition was defeated at Marathon and it returned home.

Persia then realised it would have continuing interference from mainland Greece in the Greek cities of Asia within its empire, and resolved to incorporate all peninsula Greece within its boundaries and so create an ethnic frontier. A second expedition was mounted in 480-479 BCE to achieve this, but after taking control of northern and central Greece, this also failed after defeats at Salamis, Plataia and Mykale. The warfare around the fringes of the Aegean sea went on until a peace was arranged in 449 BCE.