The second Persian invasion of Greece occurred during the Greco-Persian Wars, as King Xerxes I of Persia sought to conquer all of Greece. The invasion was a direct, if delayed, response to the defeat of the first Persian invasion of Greece at the Battle of Marathon, which ended Darius I's attempts to subjugate Greece. After Darius's death, his son Xerxes spent several years planning for the second invasion, mustering an enormous army and navy. The Athenians and Spartans led the Greek resistance. About a tenth of the Greek city-states joined the 'Allied' effort; most remained neutral or submitted to Xerxes.