What happened to Sparta?

Could you elaborate on the fate of Sparta? It was once a powerful city-state renowned for its military prowess and strict social order, but what led to its decline and eventual downfall? Did internal strife, external pressures, or a combination of both factors contribute to its demise? How does Sparta's story serve as a cautionary tale for modern societies and economies, particularly in the realm of cryptocurrency and finance where stability and resilience are paramount?