Dan 11:2

2 Now will I show you the truth. Behold, there shall stand up yet three kings in Persia; and the fourth shall be far richer than they all: and when he has grown strong through his riches, he shall stir up all the realm of Greece. 

now I tell you the truth – this will begin the “Book of truth,” introduced in Dan 10:21.

there shall stand up yet three kings in Persiaand the fourth shall be far richer than them all– the fourth, after Cyrus the Great, was King Ahasuerus (Xerses 1, 485–465 BC). In Esth 1:4 we are told that he displayed all the riches of his glory and majesty for 180 days. His palace was twice the size of his father’s, and his taste in architecture was similar, but on a gigantic scale. He gathered enormous resources through taxation, for various construction projects. The three kings who preceded him were Cambyses (530–522 BC), Bardiya (522 BC), and Darius 1 (522-486 BC).

through his riches, he shall stir up all the realm of Greece – most translations state this as “all against the realm of Greece” but the actual text reads “all אֵת the realm of Greece.” The word אֵת only denotes the accusative and is not translatable. Xerses I caused Greece to covet the riches of Persia. This is similar to the story of Isa 39, where Hezekiah showed Babylon all of his riches. This resulted in Babylon’s attack; as we read in Isa 39:5-6. Xerses 1 not only flaunted his wealth, but he also unsuccessfully attacked Greece, which eventually resulted in Persia’s fall, by Alexander the Great.