From what I understand, Persia was a powerful and wealthy nation already, while Greece was still a fledgling civilization on the outskirts of the then-civilized world, which still centered on Mesopotamia and Egypt.

So what on earth made Xerxes raise such a large army and invade Greece? Did he do it for personal reasons, for example because he was insulted, or because he was pursuing glory, or was it a rational choice in a geopolitical sense?

What did the Achaemenid Empire stand to win from invading Greece? What were their objectives?