Daniel 11:2 And now will I shew thee the truth. Behold, there shall stand up yet three kings in Persia; and the fourth shall be far richer than they all: and by his strength through his riches he shall stir up all against the realm of Grecia. - Free Bible Online

      2. three kings in Persia--Cambyses, Pseudo-Smerdis, and Darius Hystaspes. (Ahasuerus, Artaxerxes, and Darius, in Ezr 4:6, 7, 24). The Ahasuerus of Esther (see on Da 9:1) is identified with Xerxes, both in Greek history and in Scripture, appearing proud, self-willed, careless of contravening Persian customs, amorous, facile, and changeable (Da 11:2).
      fourth . . . riches . . . against . . . Grecia--Xerxes, whose riches were proverbial. Persia reached its climax and showed its greatest power in his invasion of Greece, 480 B.C. After his overthrow at Salamis, Persia is viewed as politically dead, though it had an existence. Therefore, Da 11:3, without noticing Xerxes' successors, proceeds at once to Alexander, under whom, first, the third world kingdom, Grecia, reached its culmination, and assumed an importance as to the people of God.
      stir up all--Four years were spent in gathering his army out of all parts of his vast empire, amounting to two millions six hundred and forty-one thousand men. [PRIDEAUX, Connexion, 1.4. l. 410].

JFB.