Why did Xerxes I invade Greece in 480 BCE?

Xerxes I invaded Greece in 480 BCE primarily to avenge the defeat his father, Darius I, suffered at the Battle of Marathon in 490 BCE.12

Although Xerxes initially preferred to focus on peaceful activities, he was heavily pressured by his entourage to renew hostilities. His cousin and brother-in-law, Mardonius, was a primary advocate for the invasion, supported by a faction of exiled Greeks. Mardonius may have been motivated by the prospect of becoming satrap of Greece.21

Xerxes, described as a sovereign who viewed opposition as a personal affront, eventually yielded to this pressure. He spent three years (484–481 BCE) making extensive diplomatic and military preparations for the campaign, which he treated as a major imperial undertaking rather than a minor operation. While some historians have speculated on other potential motives, such as the manifestation of royal absolutism, the desire to restore Persian prestige following the setback at Marathon remains the central historical explanation for the invasion.2