Athens and Sparta were the two city-states that started the wars. The starting of the war was when Sparta wouldn’t let Athens help them with anything. The first war broke out in 495 B.C. and lasted 15 years. Sparta forced the Athenians to return to the lands it conquered was by attacking their main city Attica. The peace agreement at the end of the war was called the Thirty Year Peace treaty. Athens was the first one to break this in many ways. One of those ways was commanding the walls of Potidaea to be torn down.
The second Peloponnesian War was called the Archidamia War. It began in 432 B.C. Te first step Sparta did was marching into Attica. It was hard to have whole battles because Sparta preferred land battles, but Athens preferred naval battles. In 430 B.C. a plague struck Athens and killed 30,000 men! At the end of this war, there was not a peace treaty.
In the third Peloponnesian War, the Persians and some other cities helped Sparta fight Athens. Athens was likely to survive because its foes didn’t want to destroy quickly. In 406 B.C. Athens won a naval victory. The Spartans took off to conquer the Hellespont because it was where Athens got their grain, and without grain, Athens couldn’t eat.