Athens and Sparta agreed to a 30 year peace after the Persian War. Athens used this time to build her empire under the leadership of Pericles.
The sea was overrun with pirates. Since the Athenians had the best navy in Greece, they said they would get rid of the pirates. This was fine until all the pirates were gone. At this time, the Athenians kept on stopping ships and collecting money. Pericles, the leader of the Athenian democracy, used the money to rebuild the Athenian acropolis that had been burned by the Persians. The Acropolis was rebuilt using marble including a shrine to the Goddess Athena. At the same time, Pericles kept a watchful eye on Sparta and built high walls [almost 7 feet thick and 23 feet tall] which connected Athens with the sea and made her the strongest fortress of that day.
The people of Sparta became angry over this. Plus the Spartans feared Athens's growing power and prosperity.
In 431 BC, Sparta declared war on Athens. One big problem occurred. The two armies had trouble finding a place to fight. The Spartans were great on land. The Athenians were a great sea power.
Sparta was located in a valley 150 miles from Athens. Male citizens had to be soldiers. Because of this, Sparta had the strongest army in Greece.
When war started, many Athenians moved from the countryside into the city walls. Overpopulation caused a plague resulting in many deaths including Pericles’. Some historians say that two-thirds of the Athenian population died at this time. Due to her weakened state, Athens and Sparta agreed to a truce called the Peace of Nicias. The peace lasted for 6 years.
The second war started when in 415 BC, Athens sent soldiers to help her allies on the island of Sicily. Athens lost but Sparta retaliated. Spartans gathered allies to fight Athens. The Persians helped Sparta by lending money for warships.
The 30 year war weakened not only Athens but Sparta as well making it easy for Philip II of Macedon to take over Greece.
Macedon was the largest city-state in Greece. Philip II became its king. Some historians believe Philip II was the smartest leader in all of history. He built up trade, built roads, helped the farmers and did a number of things to help the city-state run smoothly. As a leader he built a large army. He came up with better ways of fighting. One of these was rams for knocking down walls. He built towers for archers to shoot into the city. He also invented the catapult. Philip II and his army conquered a lot of land. He eventually conquered all of Greece. Philip II decided to fight Persia. Before Philip could carry out his plan he was murdered.