When the Spartans and Athenians led the Greek poleis to victory against the Persians in the Persian War, it was a shock to the entire region of the Mediterranean and Middle East. Persia was the regional “superpower” at the time, while the Greeks were just a group of disunited city-states on a rocky peninsula to the northwest. After their success, the Greeks were filled with confidence about the superiority of their own form of civilization and their taste for inquiry and innovation. Greeks in this period, the Classical Age, produced many of their most memorable cultural and intellectual achievements.
The great contrast in the Classical Age was between the power and splendor of the Greek poleis, especially Athens and Sparta, and the wars and conflicts that broke out as they tried to expand their power and control. After the defeat of the Persians, the Athenians created the Delian League, in theory a defensive coalition that existed to defend against Persia and to liberate the Ionian colonies still under Persian control, but in reality a political tool eventually used by Athens to create its own empire.
Each year, the members of the Delian League contributed money to build and support a large navy, meant to protect all of Greece from any further Persian interference. Athens, however, quickly became the dominant player in the Delian League. Athens was able to control the League due to its powerful navy; no other polis had a navy anywhere near as large or effective, so the other members of the League had to contribute funds and supplies while the Athenians fielded the ships. Thus, it was all too easy for Athens to simply use the League to drain the other poleis of wealth while building up its own power. The last remnants of Persian troops were driven from the Greek islands by 469 BCE, about ten years after the great Greek victories of the Persian War, but Athens refused to allow any of the League members resign from the League after the victory.
Soon, Athens moved from simply extracting money to actually imposing political control in other poleis. Athens stationed troops in garrisons in other cities and forced the cities to adopt new laws, regulations, and taxes, all designed to keep the flow of money going to Athens. Some of the members of the League rose up in armed revolts, but the Athenians were able to crush the revolts with little difficulty. The final event that eliminated any pretense that the League was anything but an Athenian empire was the failure of a naval expedition sent in 460 BCE by Athens to help an Egyptian revolt against the Persians. The Greek expedition was crushed, and the Athenians responded by moving the treasury of the League, formerly kept on the Greek island of Delos (hence “Delian League”), to Athens itself, arguing that the treasury was too vulnerable if it remained on Delos. At this point, no other member of the League could do anything about it – the League existed as an Athenian-controlled empire, pumping money into Athenian coffers and allowing Athens to build some of its most famous and beautiful buildings. Thus, the great irony is that the most glorious age of Athenian democracy and philosophy was funded by the extraction of wealth from its fellow Greek cities. In the end, the Persians simply made peace with Athens in 448 BCE, giving up the claim to the Greek colonies entirely and in turn eliminating the very reason the League had come into being.
Meanwhile, Sparta was the head of a different association, the Peloponnesian League (originally founded before the Persian wars as a mutual protection league of the Greek cities of Corinth, Sparta, and Thebes). Like Athens, Sparta dominated its allies, although it did not take advantage of them in quite the same ways that Athens did. Sparta was resentful and, in a way, fearful of Athenian power. Open war finally broke out between the two cities in 431 BCE after two of their respective allied poleis started a conflict and Athens tried to influence the political decisions of Spartan allies. The war lasted from 431 – 404 BCE.
The Spartans were unquestionably superior in land warfare, while the Athenians had an seemingly unstoppable navy. The Spartans and their allies repeatedly invaded Athenian territory, but the Athenians were smart enough to have built strong fortifications that held the Spartans off. The Athenians, in turn, attacked Spartan settlements and positions overseas and used their navy to bring in supplies. While Sparta could not take Athens itself, Athens was essentially under siege for decades; life went on, but it was usually impossible for the Athenians to travel over land in Greece outside of their home region of Attica.
Truces came and went, but the war continued for almost thirty years. In 415 BCE Athens suffered a disaster when a young general convinced the Athenians to send thousands of troops against the city of Syracuse (a Spartan ally) in southern Sicily, hundreds of miles from Greece itself, in hopes of looting it. The invasion turned into a nightmare for the Athenians, with every ship captured or sunk and almost every soldier killed or captured and sold into slavery; this dramatically weakened the Athenian military.
At that point, the Athenians were on the defensive. The Spartans established a permanent garrison within sight of Athens itself. Close to 20,000 slaves escaped from the Athenian silver mine that had originally paid for the navy before the Persian War and were welcomed by the Spartans as recruits (thus bolstering Spartan forces and cutting off Athens' main source of revenue). Sparta finally struck a decisive blow in 405 BCE by surprising the Athenian fleet in Anatolia and destroying it. Athens had to sue for peace. Sparta destroyed the Athenian defenses it had used during the war, but did not destroy the city itself, and within a year the Athenians had created a new government.