His point was that the Spartan system, as overbearing as it was, was among the first that asked people to trade tribal identity for national identity, and imposed a universal set of requirements on its citizens. He sees this as a break through, and one that much of the Islamic world is still fighting. So he views the Spartans as an important early component of the creation of the philosphical underpinnings of civilization.
I am not doing his argumnets justice. It's been three years since I read the book and I don't have a copy handy to refresh my memory.
None the less I suspect you would enjoy it.