The Peloponnesian War was a conflict fought between the city-states of Athens and Sparta from 431 to 404 BCE. It arose from power struggles and alliances within ancient Greece, primarily between the Delian League, led by Athens, and the Peloponnesian League, led by Sparta. The war is divided into three phases: the Archidamian War, the Sicilian Expedition, and the Ionian or Decelean War. The war ended with the defeat of Athens, leading to a shift in power in ancient Greece. The conflict had significant social, political, and economic impacts, weakening many city-states and paving the way for the rise of Macedonia under Philip II.