The Peloponnesian War
Part 1: In the Beginning
The Peloponnesian War was a decades-long struggle for supremacy between primarily Athens and Sparta, the two major powers of Ancient Greece. In the end, the whole of Greece got involved.
Greece's victory in the Battle of Plataea ended the Greco-Persian Wars, in 479 B.C. The following year, Athens set up the Delian League, a confederation of Greek city-states that was formed as a buffer against further Persian invasions. The headquarters was originally in Delos, which gave the league its name. In 454, Athens, by far the most powerful of the city-states in the League, became the capital city. By this time, Athens was in the habit of issuing orders to the rest of the League's ships and of demanding tribute from other League members. The tribute payments from smaller city-states only widened the gulf between them and Athens, in addition to filling the Athens city coffers with lots of money to build high, thick walls and plenty of ships with which to patrol an empire.
For by the middle of the 5th Century, Athens was at the head of an empire. Athenians commonly referred to their Athenian Empire, believing that as the inventors of democracy and the architects of the defeat of the massive Persian armies at Marathon and Plataea, they were in prime position to exert influence in the Aegean and wider world. Athens was quite happy to continue to harass a weakened Persia, in hopes that such continual harassment would help prevent further mass invasions.
The other major city-state of the Greek world was Sparta, home of the famed warriors who made names for themselves in every battle they fought, most notably at the defense of the pass at Thermopylae. Sparta had its own confederation of allies, the Peloponnesian League. (The large piece of land on which Sparta sat was called the Peloponnesus.) Sparta had had enough of the Persian Wars and preferred to focus on its own affairs.
Athens and Sparta were opposites in many ways, notably in their preferred form of government. Athens was famously a democracy, whereas Sparta was an oligarchy, ruled by a group of "strongmen." Naturally, each city-state preferred its allies to share the political philosophy of their "benefactor."
Another key way in which the two major city-states differed was in the form of their armed forces. Sparta was famous for its army; Athens was famous for its navy. The Peloponnesian War, when it came, was a start contrast between opposing military forces and strategies. Before the war was over, it would make a handful of people and places household names for centuries to come, as well as usher in a newly massive scale of warfare.
An initial struggle between Athens and Sparta began in 459, when Athens forged an alliance with Megara, a city-state on the Isthmus of Corinth. At the time, Megara was fighting with its neighbor Corinth, a member of the Peloponnesian League. Sparta thought that Athens' alliance with nearby Megara brought the Athenian presence too close to Sparta for comfort and launched a large invasion of Attica, the land surrounding Athens. A few years of heavy warfare later, the two major city-states agreed to end the fighting, in 446, in what came to be known as the Thirty Years' Peace.
Conflict flared again in 440, when Samos, a member of the Delian League, rebelled against Athens and found a willing ally in a Persian satrap. Athens closed in and stopped the rebellion. Sparta chose not to interfere. At the same time, however, trouble was brewing in nearby Corinth. Corcyra, a Corinthian colony, had revolted and won its freedom, defeating the much larger Corinthian army. In response, Corinth built up its forces, including a bigger navy, and determined to retake Corcyra. The little city-state sought help from a much larger partner, Athens, which joined the fray, against Corinth, which responded by encouraging the Athenian colony of Potidaea to revolt.
The terms of the Thirty Years' Peace were quite explicit in that Athens promised to stay out of the affairs of the Peloponnesian League and Sparta promised to stay out of the affairs of the Athenian Empire. To a majority of the Spartan assembly, Athens' actions were in violation of the Peace. Sparta determined to have its say, on the field of battle.