The document discusses the origins of the Persian Wars between Greece and Persia from 500-440 BC. It provides context on the expansion of the Persian Empire under Cyrus the Great, Cambyses II, and Darius I. This established Persia's control over Greek city-states on the Aegean coast and brought their western frontier to the coast of Asia Minor. It also summarizes the Ionian Revolt in 499 BC, in which mainland Greek city-states sent help to the Ionian states, which some see as the beginning of trouble and a catalyst for Persian invasions of Greece.