Why did Spartan society revolve around training for war?

Answer 1

The extended Spartan territory including Messenia was occupied by a serf population which always posed a threat of uprising (Spartan expeditionary forces always took seven serfs per hoplite with them as light infantry to reduce the potential for trouble while they were away).

Sparta was bordered in the north by cities initially hostile to it. Apart from its hereditary enemy Argos, it gradually beat these into submission and they became allies.

This several-hundred year history of internal and external threat turned them into a professional military society. They were enabled in this by having the serf population work for the warrior population, leaving them free to train for war.

Given this, Sparta did not actively pursue war. Their military strength was aimed at keeping internal control and deterring invasion. Usually they were reluctant to go to war or interfere in other cities, and needed a lot of pressure from their allies to go beyond diplomacy to declaring war.

Answer 2

It had taken over the southern Peloponnese Peninsula and converted the landowners to serfs who delivered half their produce to Sparta. This allowed the Spartan citizens to divert their activity to preparation for warlike activities - to protect the territory from other Greek invaders, and to keep the large serf population under control.

Answer 3

Each Greek city-state had to focus on military skills to survive. But Sparta had taken over the southern Peloponnesian Peninsula and turned the peoples into serfs who delivered half their produce to Sparta, and so the Spartans could turn their activities from producing food themselves, towards keeping the serfs under control and defending against external threats.