
“Master, it is not fitting that the Athenians should go unpunished for their deeds, after all the evil they have done to the Persians.”
Herodotus, The Histories; Book 7 Chapter 5 Sec.1
Had the Persian king Darius defeated the Greeks at the battle of Marathon or even his son Xerxes conquered the Greeks the world would be a much different place than we know today. It was the Greeks who founded democracy and who created great works of art and literature, such as the Iliad and the Odyssey. It is from these stories and ideas that we have built our world and our culture. The Persians had no concept of democracy and cared not for the good of the people only for the power of their king.
It is hard to say whether democracy could have survived through the tyranny of Persian rule. Whether or not Greek literature could have continued to be written and carried on through the ages. Most likely the Persians would have crushed such thinking and ideas with terrible and swift punishment. Those who spoke of freedom would be hunted down and killed and those who wrote stories of the glory of Greece would find the same fate. 
Now that Greece is firmly under Persian control, what will become of the lands to the east? Phillip II would be unlikely to emerge as king of Macedon and unite the Greek city states. His son Alexander the Great would not lead a great campaign to Hellenize the east. Kandahar would not be Kandahar, which is the Afghan name for Alexandria, and there would be no Great Library at Alexandria in Egypt full knowledge and wisdom from all over the world.
How far west would the Persians expand? Could anyone have stopped them? The Roman Republic is in its infancy and still has a powerful rival, Carthage in North Africa to deal with. Had the Persians and Carthaginians allied against Rome she surely would have fallen before she could barely walked. All that was Roman would have been lost and the great ideas and philosophy of the next twelve hundred years would be lost. Julius Caesar would have never crossed the Rubicon, never came, never saw, and never conquered.
Th
e simple defeat of the Greeks has completely changed the course of history and nothing would have occurred as it did. Take for example the months of the year. July named for Julius Caesar would be known by another name as well as August named after Caesar Augustus, also known as Octavian before becoming emperor in 27 B.C. Most other months in the Georgian calendar which we most commonly refer to are derived from Latin or Roman gods. Had the Roman Empire not come to such prominence as it did we would know nothing of Latin let alone name our months after emperors who never ruled and gods who were clearly inferior to their Persian counterparts. Also take into consideration the English language; most of its words are derived from Latin or Greek. How could this language be formed if everyone was speaking the language of the Persians?
Medicine, Theater, and philosophy would be much different today as well. These new ways of thinking in 500 B.C. were pioneered by Greeks during the classical age that followed the Persian wars. Meaning… they made it all up, developed it themselves. Were it not for these Greek thinkers and doers many of the social norms that occur today without a second thought would be strange and alien to us if we even see them happen at all. We could only hope that the works of Plato, Aristotle, Sophocles and Euripides would be forgotten because it is likely that they never had the chance to share their work in writing.
Many of the ancient building such as the Parthenon were built during this time. Imagine the Athenian Acropolis without the massive ruins of the Parthenon sitting atop its peak. Though the Greek city-states fought amongst themselves for around 30 years they were still able to construct these wonders and write priceless works of literature such as Sophocles’ Oedipus the King.
“The only true wisdom is in knowing you know nothing.” -Socrates
The philosophers of this time still influence us today. Most of their work is still relevant to modern thought and some have said the no one has come close to the creative range of Aristotle with the exception of Leonardo da Vinci. Socrates, though put to death by his fellow Athenians, might have had a chance to get his work out to the public but the chances that he would have even existed are scarce. He would not have had an opportunity to think the way that he did because he would have grown up in a society that belittles independent thought.
In today’s modern world we can see Greek influence everywhere we look. Washington D.C. for example is full of marble and granite colonnades and domes which were clearly influenced by Greek and Roman architecture. Our own democracy in the United States of America is based on the Roman Senate and assemblies of the people. Those themselves were based along the lines of the Greek city-states’ democratic ideals. How could this have come about if it were not for the audacious thinking of the ancient Greeks? Had the Persians defeated and conquered Greece in 480 B.C. none of these social norms would exist. Most likely we would still be living in a feudal system of government of Lord and serf, King and subject. Freedom of speech? Private property? What do those words even mean?

“The foundation of happiness is freedom that of freedom is courage.” Thucydides