Also consider the political differences between Athens and Sparta. Athens had a sloppy democracy that amounted to little more than mod rule between the many aristocratic families. This is why disagreements often devolved into civil wars that ended in re-establishment of a tyranny. Then it was never long before the families that lost the civil war would join together to chase out the tyrant and re-establish a sloppy democracy that would devolve into fighting again.

The Spartans had more of a system of checks and balanced that resembled a primitive form of republicanism. They had an elected council of ephors that checked the power of the king. They had a "Gourgias" which was an elected council of elders that handled civil law and acted as a supreme court. And then they had the "Assembly" (which comprised all the Spartan men over 20) which had final say in all matters of war and peace. Though voting within these groups amounted to shouting over each other at the feast table (Aristotle called it childish) it gave them a sense of stability that the other city-states never had.

There is also a sense of national pride in Sparta that you don't see elsewhere. The city folk of Sparta and the surrounding countryside of Lacadaemon considered themselves as one people whereas Athens and rural Attica had a broader cultural line drawn between them.