The Persians continued to reduce the cities along the west coast that still held out against them, before finally imposing a peace settlement in 493 BC on Ionia that was generally considered to be both just and fair. The Ionian Revolt constituted the first major conflict between Greece and the Achaemenid Empire, and as such represents the first phase of the Greco-Persian Wars. Asia Minor had been brought back into the Persian fold, but Darius had vowed to punish Athens and Eretria for their support of the revolt. Moreover, seeing that the political situation in Greece posed a continued threat to the stability of his Empire, he decided to embark on the conquest of all of Greece. The first campaign of the invasion was to bring the territories in the Balkan peninsula back within the empire. The Persian grip over these territories had loosened following the Ionian Revolt. In 492 BC, the Persian general Mardonius re-subjugated Thrace and made Macedon a fully subordinate part of the empire; it had been a vassal as early as the late 6th century BC but retained a great deal of autonomy. However, in 490 BC the Persian forces were defeated by the Athenians at the Battle of Marathon and Darius would die before having the chance to launch an invasion of Greece.