Did you really propose immigration as a solution to Spartan problems? No sir. Immigration was the cause of demise to all ancient governments including the Romans.\n\nOne thing you forget to mention about the Spartan society is how obssesed they were with economic disparity. To force sobriety they would accuse one another of undeclared wealth which would force them to pay for the city's infrastructure and reforms. They wasted tons of money trying to hide it so they weren't particularly keen to the rigurous system, but it was their city so while this was true they didn't care. The Spartans had an excelent system but it was too expensive.\n\nTheir problem was like any other greek kingdom. Economics. The  fall of the Delian League left the Spartans with too much land to rule under a centurial system concieved for just the Peloponnese. This created political instability, poor quality foreign governments and eventually famine, with the exception of Macedon, Greece became a shadow of its former self.\n\nSurrounded by a cilmate of dire economic conditions the Spartans unable to support the growing inflation suddenly percieved the life outside of the strict highly expenssive Spartan society was increasingly more appealing, and began to leave the city for a live of carelessness who gets it keeps it free for all, until eventually were but some few thousand men inside Sparta to keep it safe.