The great harlot is the perversions of this world of which the US is the premiere exporter to the world. We live in the midst of the great harlot and we seem to marvel at her instead of be repulsed.The Great Harlot is a religious system—false Christianity, not the civil system.
Read your Old Testament. When Israel worshiped false gods, instead of the true God, God referred to them as committing harlotry and spiritual adultery.
*Revelation 17:6*
And I saw the woman, drunk with the blood of the saints, the blood of the martyrs of Jesus. When I saw her, I marveled greatly.
The angel had to instruct John to see past the surface.
*Revelation 17:7-8*
But the angel said to me, “Why do you marvel? I will tell you the mystery of the woman, and of the beast with seven heads and ten horns that carries her. The beast that you saw was, and is not, and is about to rise from the bottomless pit and go to destruction. And the dwellers on earth whose names have not been written in the book of life from the foundation of the world will marvel to see the beast, because it was and is not and is to come.
Notice that the beast is a false messiah. "Was, is not, and is to come" is a contrast to Jesus to whom it is said, “I am the Alpha and the Omega,” says the Lord God, “who is and who was and who is to come, the Almighty.”
~ Revelation 1:8
The beast tries to copy our King, but falls short.
Today, the church is often jumping into bed with the harlot and they don't even recognize it because they foolishly marvel at the riches it offers.