In Assassin's Creed Odyssey, which ancient Greek war began shortly before the game's main story?

The Peloponnesian War began shortly before the main story of Assassin's Creed Odyssey.

Assassin's Creed Odyssey is set in ancient Greece during the 5th century BCE, with its central events taking place during the conflict between Athens and Sparta. The war began in 431 BCE and continued, with interruptions, until 404 BCE. The game's opening Battle of Thermopylae sequence occurs earlier, in 480 BCE, during the Greco-Persian Wars.

The player character is a descendant of Leonidas I and can choose either Kassandra or Alexios as the playable hero. The story travels across the Greek world, including Attica, the Peloponnese, the Aegean islands, and Macedonia.

The main conflict is sometimes confused with the earlier Greco-Persian Wars because the game opens with Thermopylae. That battle is a historical prologue; the principal campaign is set during the Peloponnesian War.