The Greeks (and Greek speaking barbarians in the region) had done immensely well with the reforms pioneered by Athens ~ credit unions, plantings of olive trees, fostering of new invention to make work easier, etc.
The Persians didn't have a chance!
Sure, Alexander was a strategic and tactical genius, but Greece had 4 to 5 times the population that Persia controlled.The population of Greece was something under 1 million (circa 800,000) by the time of Alexander. The Persian empire was enormous, and controlled the Fertile Crescent and Egypt, and was much larger than that. But the Persian army was polyglot, and included Greeks from Anatolia; Greek speakers had spread throughout the Persian empire, and that probably helped when it came time to put the hammer down during the Central Asian campaign. But Alexander relied also on native troops of various nationalities, just as the Persians had.