The Peloponnesian War was fought between the two most powerful forces in Greece, the Peloponnesian League and Sparta, and the city-state of Athens and its allies. What we know about the war and the subsequent collapse of the Athenian navy is because of the research by Greek historian Thucydides. Athens was eager to prove that they were unbeatable, while the Peloponnesians wanted the total destruction of Athens. At the time. the Peloponnesians had the more powerful army, while the Athenians were the uncontested masters of the Mediterranean Sea.
Both sides claimed to be fighting for freedom. The war lasted from 431 B.C. to 403 B.C. Athens and its allies were called the Delian League. As the leader of the Delian League, Athens demanded tribute in the form of money or ships from its allies. The Delian League protected and eventually liberated the Greek city-states from the Persians. However, once the Greek cities were liberated from the Persians, the Athenians forced them to stay in the league under their control. The Spartans claimed they were fighting to free Greece from Athenian imperial domination. In fear of Athens rising power, it was the Spartans who attacked first.
At the time, Athens was under the control of General Pericles. Pericles was responsible for the cities great cultural, architectural, and military gains. Under his leadership Athens had become the cultural center of Greece. Architecture had flourished, including construction of the Parthenon, an amazing temple dedicated to the goddess Athena. In addition, Pericles connected Athens with the port city of Piraeus with long walls in case they were attacked. Pericles was an aggressive military leader, and it is believed that his political ambitions incited the two sides into war. The war broke out in 431 B.C., and continued for ten years. The entire country of Greece participated. During the first few years Sparta ravaged the countryside surrounding Athens, an area known as Attica.
Eventually, as the fighting got closer, Percilies ordered all of the people of Attica to take shelter in the cities of Athens and Piraeus, and between the long walls which were 5 miles long. The population doubled overnight. Pericles strategy was successful in stopping the superior Spartan army, but it had devastating effects on the morale of its citizens as they could do nothing to save their homes and farms from destruction. Making things worse, Athens was overcome by the plague twice and it lost 1/3rd of its population, including Pericles. After losing Pericles, Athens gradually lost control over the sea. The first war was fought to a stalemate.
Then, in 413 B.C., Athens send out an expedition to conquer the island of Sicily. This resulted in a resumption of war between Sparta and Athens. After two years of fighting Athens suffered tremendous losses, including all of its ships. At this time Athens' power was diminished terribly. Before long, Athens allies revolted and the city-state was broke. At the same time, Sparta was receiving financial support from the Persians, who wanted to make sure that they were successful. A year later, Athens surrendered and Sparta set up their own government in Athens called the Rule of Thirty or Thirty Tyrants.