What was the downfall of the Spartans?

Could you elaborate on the reasons behind the downfall of the Spartans? Were there specific factors, such as strategic missteps, internal conflicts, or external pressures, that contributed to their decline? Additionally, how did their military prowess, which was once renowned, fail to sustain their power and influence in the long run? Understanding these aspects may provide valuable insights into the complexities of ancient civilizations and their rise and fall.