By all calculations Sparta should have lost the war. Athenians had strong leadership and the money to finance a war. Their Navy ruled the seas and was virtually unbeatable on the seas. Sparta had little money, weak leadership, and no navy. Their only true strength was a strong ground force. Sparta is able to win the war by obtaining Persian monies as support, a strong leader (Lysander), and reaping the rewards of the Athenians mishaps. Athens leadership failed to realize the cost of a lengthy war. Their were several internal conflicts that ranged from political leaders private ambitions, inconsistent policy, and revolts of allied city-states.
The Athenians were unable to maintain her leading allies. One prime example is there relationship with the Argives. They would be engaged in battle with them and then would make an alliance with them. (5.40) The Argives formed the alliance with Athens because they thought they would be isolated when Boeta allied with Sparta.
The Athenian strength and oppression pushed the Argives into making a truce and alliance with Sparta. (5.61,77-79) This failure to keep strong allies faithful and loyal would prove as distracting as the revolts Athens suffered.
The Athenians had to constantly deal with revolts within their allied city-states. These revolts taxed the Athenians resources and distracted them from the task at hand. The revolts occurred due to Athens oppression of liberty as promised and fear of her growth. (3.10-12)
The Mytilenes revolted and Athens had to send 40 ships to try and retake the city. During the time Athens was under siege by the plague. (3.3) They also sent 30 ships out and after completing several task sent all but 12 back to Athens. In Leucas the Athenians lost troops and a commander. (3.7) Sparta also used this unrest of Athens city-states...