Stop talking about Sparta as a real power in that era. After the defeat of Leuctra (371 BC), Spartan power was just a (Sweet? Bitter?) memory. From then on, Sparta was just a toy in the political game of Macedon -first- and Rome -after- for the domination of Greece; its military power reduced to almost nothing, and its legendary discipline becoming a tourist attraction of the ancient world.

Sparta allied the Romans as soon as they stepped on Greece, and when Rome stopped needing Spartans, declared war on them and defeated them with ease, forcing Sparta to seek help in the Achaean League -which treated them in a similar way- to finally fall -as the whole of Greece- in Roman hands.

It had been a long long time since the epic times of Leonidas.