The Greco-Persian Wars, also called the Persian Wars, were a series of armed conflicts involving various Greek city-states and the Achaemenid Empire from 499 BC to 449 BC. The precipitating collision between the fractious political world of ancient Greece and the enormous empire of ancient Persia had begun when the Persian king Cyrus the Great conquered the Greek-inhabited region of Ionia in 547 BC. As they struggled to exert authority over the independent-minded Ionian cities, the Persians appointed Greek tyrants to rule each of them, though this would prove to be the source of much trouble for the Greeks and the Persians alike.