What caused the Sparta and the Persian war start?

Answer 1

There was no 'Spartan-Persian' War. There were two main Persian invasions, in 490BC by Darius I and 480BC by Darius' son Xerxes I. Sparta arrived too late at the main battle of the First invasion which the Athenians crushed at Marathon. In the second Persian war, Sparta sacrificed their best men along with their King (Leonidas I 490-480BC) at the battle of Thermopylae. 700 Thespians and 300 Thebans also gave their lives to delay the Persian advance. The Persians marched onto Athens which they sacked while the Athenians were safe on the island of Salamis. The Athenian fleet then defeated the vastly outnumbering Persian fleet at the battle of Salamis. The enormous land army engaged with 10000 Spartans leading about 30000 other Greeks at the battle of Plataea in 479BC and defeated the Persian invasion which then returned home to Sardis.

The cause of the wars were simply Persia's desire to expand her empire and although many Greeks 'medized' and let the Persians occupy, many would not. Sparta's great belief in tradition (which did ultimately lead to her collapse) and her law of 'Never surrender' meant that submitting to the Persian occupation was not an option. However, Sparta was reluctant to engage in the war, and many states had raised arms long before Sparta.