The differences between Athens and Sparta were caused by the geographical location, they were quite far apart so it should be expected that they had different societies. Another reason was that they were both founded at different times, by different people.
They were both independent city-states in southern Greece. The Spartans were rural, living off the produce of a serf population and devoting themselves to training for war. The Ahenians had to do their own production and their war training in their spare time. The Spartans were stolid and cautious, the Athenians were adventurous.
The war against Persia. It united all of Greece, including Athens and Sparta.
The caused of lack of trust between Athens and Sparta were suspicion. As Athenian empire became rich and powerful, other city-states such as Sparta grew suspicious of it aim. Led by Sparta, they start join forces against Athens.
Political instability and civil war caused by the fighting between Sparta and Athens and the delian League.
Athens sent troops to help Sparta put down a revolt by their serfs. The Athenians started to show signs of favouring the serfs, so the Spartans sent them home, with lasting resentment on both sides.
The Peloponnesian War was caused by Athens slowly creating an empire under Pericles, an Athenian general. Sparta did not want only one city-state to be able to control all of Greece, so they decided to attack Athens, causing the Peloponnesian War.
Rising tensions between the Peloponnesian League led by Sparta and the Athenian Empire which was pushing them too far in Athens' over-aggresive policies.Athens, having turned the alliance against the Persian Empire into an empire of its own, interfered in the other cities to extend its influence. The Peloponnesian League led by Sparta, some of whose members were targeted by Athens, gave an ultimatum for this interference to cease. Athens persisted and war ensued.The fear of the growing strength of Athens.
A contest between Sparta and its allies and Athens and its empire 431-404 BCE, which caused great devastation throughout the Hellenic world from Sicily to Asia Minor. The Spartan side, with Persian financial backing, overcame the Athenian side and Athens was divested of its empire.
Their military defeat & their loss in the Peloponnesian War. Sparta burned all of the Athenian food supply and a plague also occurred in Athens which killed 1/3 of the population.
Athens and Sparta were independent City-States and therefore were not especially close. However, the Greeks did unite to repel foreign invasions. One of the reasons that Sparta and Athens went to war (The peloponnesian war), was because after the city of Athens was destroyed by Persian invaders, the Athenians stole large sums of money from the Delian League to rebuild their city (and also some of their most famous modern wonders, such as the Parthenon), which was a national treasury set up by the primary City-States of Greece. This action enraged the Spartans in particular, and caused the war.
In about 460 BCE, after the Persian invasion had been repelled by the combined Greek forces, Sparta was facing a revolt by its serf population in Messene, and making heavy weather in putting it down. Athens offered to help and sent an expeditionary force to reinforce the Spartan forces. The Athenians were very adventurous in their operations, and showed up Spartan methods, which was based on trying to force a pitched battle with an elusive opposition which declined to make itself such a target. There is also a suggestion thet the Athenians showed some sympathy for the Messenians. The upshot was that Sparta invited the Athenians to go home, and the usual cooperative spirit between the two cities soured. After peace was finally made with the Persians in 449 BCE, Athens converted the anti-Persian Delian League which it led into an empire of its own, continuing to levy the war fund from the 200 cities of that league to use for its own benefit and maintaining a strong navy to enforce the annual collection of money. With this strength, Athens aggressively interfered in the affairs of the cities to which Sparta was allied in the Peloponnesian League, particularly Corinth. The Peloponnesian League members urged Sparta to help them stand up to Athens. A cocksure Athens persisted in interfering in other cities, and this came to a head when Athens banned Megara, a Peloponnesian League member, from trade with cities in its empire, which would destroy Megara. The Peloponnesian League demanded Sparta act, Sparta demanded Athens back off, Athens refused, war ensued.
Cooperation between Sparta and Athens during the classical Greek era created peace and prosperity in Greece while conflict between Sparta and Athens broke ancient Greece and began the downfall of the society. These events defined the course of ancient Greek history.
Athens lost the Peloponnesian War because it was overconfident. It took severe losses over the unexpected 27 years of the war, and eventually Persia bankrolled at competitive fleet for the opposing Peloponnesian League led by Sparta. Athens lost its fleet, and so was starved into submission.