Battle of Leuctra
In 371 BC, the Spartans were defeated in the Battle of Leuctra. As a result of that defeat, Sparta's allies revolted and the helots of Messenia were freed. Afterwards, the Spartan economy became less able to support professional soldiers, and inequalities between supposedly equal citizens increased. As a result, the reputation of Sparta, either as a military success or as a guide in domestic affairs, diminished substantially.