Prince of Greece Part 1
In Daniel 10:20 it reads; Then he (the angel) said (to Daniel), “Do you know why I have come to you? And now I must return to fight with the prince of Persia; and when I have gone forth, indeed the prince of Greece will come.” (Italics mine)
The prince of Persia is a spiritual principality. He is so powerful that the angel sent to Daniel needed help from the arch angel Michael to be able to get to Daniel (verse 13), and he was going to have to fight going back as well. The physical manifestation of the prince of Persia outworked itself through the Persian empire, but the power behind this empire was spiritual. Likewise the angel talking to Daniel said that once he had gone forth then the prince of Greece would come (another spiritual principality).