Revelation mirrors Daniel in a lot of ways. Daniel was obviously a favorite of John's as he uses Daniel's symbolism a lot in Revelation.
"Fornication" as used by John means "Idol worship" or the worship of a false religion. The "kings of the earth" which are the rich Arab Oil Kings fornicated (or worshiped/served Islam).
If you remember back to Daniel 5:
[SUP]3 [/SUP]Then they brought the gold vessels that had been taken from the temple of the house of God which had been in Jerusalem; and the king and his lords, his wives, and his concubines drank from them. [SUP]4 [/SUP]They drank wine, and praised the gods of gold and silver, bronze and iron, wood and stone.
The next thing that happened was God's finger writing on the wall and it was curtains for Babylon. Please note that Belshazzar ordered the holy vessels to be taken and filled with wine and they all got drunk. After this they praised the "god of riches/wealth."
Now look at how John puts it, obviously thinking about Daniel and original Babylon.
“Come, I will show you the judgment of the great harlot who sits on many waters, [SUP]2 [/SUP]with whom the kings of the earth committed fornication, and the inhabitants of the earth were made drunk with the wine of her fornication.”
What is the source for the wealth of the Arab Kings? What is the rest of the earth buying from these sheiks? They aren't literally getting drunk on Saudi wine, they are getting rich on Saudi Oil. The west has looked past a lot of Saudi crimes and treatment of women, minorities, Christians, etc all for oil. If the Saudi's didn't have the most oil of any country, nobody would talk to them.