The Sacred Band was instrumental, even, in destroying Spartan hegemony, which championed oligarch regimes, and beginning a period of Theban hegemony, which championed democratic regimes.

This is still one of my favorite historical exchanges of all time:

The Theban force was heavily outnumbered by the Spartans opposite them. The Sacred Band numbered some 300 hoplites, while the Spartan garrison consisted of two companies (mori), meaning that the Spartan force contained between 1,000 and 1,800 hoplites. Plutarch reports that one Theban soldier, upon seeing the enemy force, said to Pelopidas “We are fallen into our enemies’ hands,” to which Pelopidas replied “And why not they into ours?” Pelopidas then ordered the Theban cavalry to charge while the infantry formed up into an abnormally dense formation. When the two phalanxes came together, the compact Theban formation broke through the Spartan line at the point of contact, then turned to attack the vulnerable flanks of the Spartans to either side. The Spartan force broke and fled, although the Theban pursuit was limited by the proximity of Orchomenus.