What wars are called internecine wars? Why did they weaken Greece?

Wars – Civil strife is a conflict that takes place within a country, associated with the struggle for dominion and land. So in ancient Greece, in fact, throughout history, there was an internal struggle and rivalry between the policies. The most ardent opponents were Sparta and Athens. In 431 BC. the unions of the Greek city-states led by Athena and Sparta began a war between themselves, which ended with the victory of Sparta.