This decay occurred because Sparta's population declined, change in values, and stubborn preservation of conservatism. Sparta ultimately surrendered its position as ancient Greece's preeminent military power.

When did the Spartan empire fall?

The decisive Battle of Leuctra in 371 BCE ended the Spartan hegemony, although the city-state maintained its political independence until the Roman conquest of Greece in 146 BCE.

Why did the 300 Spartans lose?

If the phalanx broke or if the enemy attacked from the side or the rear, however, the formation became vulnerable. It was this fatal weakness to the otherwise formidable phalanx formation that proved to be Leonidas' undoing against an invading Persian army at the Battle of Thermopylae in 480 B.C.