But the very events of this struggle had by now exacerbated the disagreement between Greeks and barbarians, which will henceforth be one of the fundamental reasons of Greek history, and had extended it to the motherland, with the repercussions that the events of that war had there., and in particular the massacre of Miletus. Immediately after the Ionian insurrection was put down, the Persians resumed expansion in the Balkan peninsula. Mardonius, sent to Thrace with an army and a fleet, reaffirmed the Persian dominance on the northern shores of the Aegean and also in Macedonia (493). The difficulties that the army encountered in its march, the losses it suffered from the attacks of the Thracian tribe, the serious damage that the army had due to a storm near Athos persuaded Darius to follow, to implement his program, a different way. Data and Artaferne were sent with a naval team and an army across the Aegean directly against the two cities that alone had rescued the rebel Ionians, Eretria and Athens (490). Eretria was, after a few days of siege, captured and set on fire. But when the Persians landed on the coasts of Attica, the Athenian forces under the orders of Miltiades met them and reported the famous and decisive victory of Marathon, which forced them to abandon the enterprise, embarking immediately to return to Asia. The victory was due to the fierce resolve of the Athenians, the audacity and skill of the commander, the superiority of Greek tactics, which opposed the phalanx of the hoplites to the undisciplined masses of the Persians.
Persia, after Marathon, did not despair of victory, but recognized that greater preparation was required. The war was resumed by Darius’s successor, Xerxes, who himself moved in command of very considerable forces on land and sea and, having passed the Hellespont on pontoon bridges, proceeded along the southern coast of Thrace towards the Hellenic peninsula. The victory of Marathon encouraged the Greeks to resist. At the head of the resistance were the two major Hellenic powers, Sparta, at the head of his league which included most of the Peloponnese, and Athens. In the interval between the battle of Marathon and the expedition of Xerxes, the Athenians, sensing the danger of a new Persian assault and recognizing that security from new aggressions could only be achieved by conquering maritime superiority, they had, at the advice and inspiration of Themistocles, created a great naval army composed of triremes; and yet, despite their maritime superiority, they did not hesitate to accept Sparta’s hegemony. The allies felt they could not defend Thessaly and established their first line of defense at Thermopylae, where the Spartan king Leonidas was sent with a small corps of troops, awaiting more forces to prepare, while the federal fleet crossed in the nearby, at the Artemisio, at the northern end of the island of Euboea. The Persians arrived in the good season of 480 in Thessaly and then proceeded to Thermopylae, while their army was positioned in front of the Greek on the coast of Thessaly near Afete. Xerxes forced the passage of Thermopylae very quickly, before help arrived for Leonidas, who fell with his three hundred Spartans in the field. This forced the Greek army to abandon the position of Artemisius and gave Xerxes the possession of all central Greece: where the Boeotians, averse to their Athenian neighbors, certainly passed over to his side. The Athenians had to clear out their city, which was taken and sacked by the Persians. But the Confederates did not lose heart; their fleet brought back to the island of Salamis, thanks to the seafaring expertise of the Greeks, their value, the excellence of their ships and in particular of the Athenian triremes, a great victory. After that, Xerxes gave up naval warfare, but believed he could continue the land war by leaving the army under Mardonius’s command in Greece. This army was destroyed the following year by the Confederate hoplites, in the battle of Plataea (479). This battle definitively demonstrated the superiority of the Greek armies and their tactics over the barbarian masses, that superiority that was to lead the Greeks to conquer the Persian empire. Even by sea, the advantage lay on the side of the Greeks. But the Persians had excellent Phoenician armies; but the Phoenicians of Asia did not fight for their freedom or expansion, like the Phoenicians of Carthage, who were therefore worthy rivals of the Greeks of Sicily, yes for a foreign dominion and under the supreme direction of foreign officers. What, all things being equal, made them inferior to their adversaries. Still in 479, while the army was winning at Plataea, the Confederate fleet pushed on the Asian coast, and here in Mycale, near Miletus, it defeated the barbarians by land and sea and called the brothers of Asia to freedom. The following year at the beginning of spring the Confederates took possession of Sesto on the Hellespont, thus virtually excluding the Persians from Europe.