The Peloponnesian war between Athens and Sparta took place over several decades and can be segregated into three main wars: a) 460 to 445 BC, b) 431 to 421 BC, and c) 415 to 404 BC. Each of these wars were fought between Athens and its empire and Sparta with its Peloponnesian league allies. Considering the large number of states involved, there were several influencing factors that added to the build up to the beginning of the war. I believe that the main cause for the war was the insecurity and power struggle between Athens and Sparta to gain political and military advantage in Helas.
Thucydides, an Athenian aristocrat who lived during the period of these wars is the main source of information for historian as he documented the wars in his book The Peloponnesian War . He claims that it was Sparta’s insecurity over the growing powers of Athens that were beginning to reach beyond the Delian league. However, Thucydides, being an Athenian, is most likely to have a biased view of the causes of war and should not be considered as an absolutely reliable source. I consider both, Sparta as well as Athens to be equally involved in beginning the war. In fact, Athens had more reason to subdue Sparta.
There were several insecurities within both states. Sparta was facing constant revolts by its slaves and it expected that this majority of its population would help an enemy in case of an invasion. It suspected that the slaves were being influenced by the democratic principles being propagated by Athens. On the other hand, Athens relied heavily on its navy which needed huge spending to maintain. Athens got this money from allies and feared that they would change sides and support the lesser demanding Sparta. As a result, both the states felt the need to subdue its rival and gain an advantage in the region. This would give both, Athens and Sparta, reason to resort to tactics that eventually led to the war.
These differences between Sparta and Athens existed for a long time before the Peloponnesian wars and had been the cause of constant political tensions between the two states. The other states in the region were always being influenced and lured by each side to switch alliances. This always kept the balance of power swaying from one side to another and developed a deep sense of mistrust between Athens and Sparta who were always looking for ways to downplay each other. The mistrust was equal on both sides and was one of the causes of war.
The first Peloponnesian was took place from 460 to 445 BC of which there is very little data available in history. However, we know that it ended in a peace treaty being signed which lasted for a turbulent 30 years before the next big war took place. This shows that although Sparta and Athens despised each other, they were willing to maintain peace, as long as their individual empires and leagues were not challenged by the other. It was this factor that led to Athens and Sparta being influenced by Corcyra and Corinth, respectively, into waging war against each other.
When the conflict over Epidamnus began in 433 BC, Corinth tried to intervene and regain it from Corcyra. Corcyra asked Athens to help them in making sure that Corinth did not send in forces to Epidamnus and Athens agreed. In response, Corinth, which was a major ally of Sparta, asked Sparta to declare an open was against Athens if it wanted to remain the leader of the Delian league. As a result, both the sides got an opportunity to wage an all out war against its rivals, something that they were not able to do for the last 30 years. In truth, Corinth had been looking for a reason to curb Athens’ growing power but could not afford to go to war by itself. Hence, it lied to Sparta that Athens had broken the truce, when, in fact, Corinth had broken the treaty.
Although it may be argued that it was Corinth the ‘tricked’ Athens and Sparta to go to war with other, I believe that the states were just waiting for a reason that seemed fair enough to wage a war. The fact that neither Athens attempted to clarify its stance when Sparta declared war, nor did Sparta seek any answers from Athens before declaring the war. Hence, it can be said that the long standing differences between Athens and Sparta led to the Peloponnesian war and not the influence of a third state.
Thucydides. The Peloponnesian War. Trans. Steven Lattimore. Indianapolis: Hackett Publishing Company Inc., 1998.