The Theban Hegemony lasts from the Theban victory over the Spartans at Leuctra in 371 BCE to their defeat of a coalition of Peloponnesian armies at Mantinea in 362 BCE, though Thebes seeks to maintain its position until finally eclipsed by the rising power of Macedon in 346 BCE.Externally, the way had been paved for Theban ascendancy by the collapse of Athenian power in the Peloponnesian War (431 - 404 BCE), through the weakening of the Spartans by their oliganthropia (demographic decline) and by the inconclusive Corinthian War (395 - 386 BCE).
Internally, the Thebans enjoy two temporary military advantages:(1) The leaders of the Theban oligarchy at this time, Epaminondas and Pelopidas, are fully committed to an aggressive foreign policy and can be relied on to win any battle and(2) The same leaders have instituted tactical improvements in the Theban heavy infantry (e.g.
longer spears, the use of a wedge-shaped formation of spearmen), which has yet to catch on among their rivals.
