Why did little Greece manage to resist the mighty Persia?

In Greece, despite its small size, there was a high population density, developed crafts and democracy, and before meeting the Greeks, the Persians defeated mainly Eastern despotism or made them their vassals. The Greeks had an army of heavy infantry – the hoplites. It was called a phalanx. The Persians had never encountered this kind of army before before the Battle of Marathon in 490 BC. In it, they suffered a heavy defeat, and then were defeated in the naval battle of Salamis and in the battle of Plataea.