The Peloponnesian War was two wars with a short peace in between. It effectively destroyed democracy in Greece. It began with great enthusiasm, yet ended disastrously for Athen's democracy. Greek philosophy after this taught that benevolent kings ruled best.
The Peloponnesian War consisted of two conflicts between Athens and its allies and Sparta and its allies lasting from 431 to 404BC with a short peace between them from 421 to 413BC. At the beginning of these wars there was great enthusiasm and nationalism on both sides but as time progressed this changed and the people on both sides became despondent. In the end Athens and her democracy were conquered by Sparta and placed under a tyrannical oligarchy.
Two of the major Greek philosophers to come to prominence during this time were Socrates and Plato. They had a significant impact on the way Greek philosophers would think after the end of the Peloponnesian Wars. Many of the democratic ideas that had been held before the wars would be changed by the discussions that Socrates and Plato brought forth.
Prior to the Peloponnesian Wars, many in Greece believed the voice of the people or the demos was the best voice to listen to because of the input of many people on a topic. However philosophers beginning with Socrates began to question this because it had been democratic ideas under Pericles that had got the people involved in the Peloponnesian Wars.
Socrates began talking about the idea that knowledge was best reached by the elenchus and dialectic. The elenchus was the idea that the truth of something was best reached by cross examinations of an opponent. The dialectic involved searching for truth by arguing conflicting ideas with an opponent until they were shown to be wrong.
Plato was the student of Socrates and was significantly impacted by the decision of the restored Athenian Democracy in 399BC to execute Socrates. Plato put forward the idea that society needed to be divided based upon intellect, physical strength of an individual, and displays of courage or bravery. Plato challenged the concept that the people should rule themselves in the city-states and promoted the idea that only the best or the aristocracy should rule the city-states.
The result of this idea, philosophers after Socrates and Plato began to hold the idea that benevolent kings or dictators who had been trained for life were best suited to rule nations. This would be especially seen in the later writings and teachings of Plato's student, Aristotle, who became the teacher of one of the world's greatest kings, Alexander the Great.