So, how was Rome a prostitute?
The RCC is not God's kingdom, as it is no part of this world...the battle spoken of in Revelation 17 is with Jesus Christ himself and his heavenly army...
"These will battle with the Lamb, but because he is Lord of lords and King of kings, the Lamb will conquer them. Also, those with him who are called and chosen and faithful will do so.”
And we know that John is not speaking about Rome, by what John says in verses 10,11...
"And there are seven kings:
Five have fallen, one is, and the other has not yet arrived; but when he does arrive, he must remain a short while. And the wild beast that was but is not, it is also an eighth king, but it springs from the seven, and it goes off into destruction."