The kings of the earth committed fornication with the Harlot both because of the allure of her harlotries, but also because she reigns over the kings of the earth. Throughout history, she has wielded powerful influence over various rulers of nations beyond Babylon. Fornication is ἐπόρνευσαν [eporneusan] , meaning to prostitute, practice prostitution or sexual immorality generally, but also used figuratively to denote the practice of idolatry (Hos. Hos. 9:1; Jer. Jer. 3:6; Eze. Eze. 23:19; 1Chr. 1Chr. 5:25).1
To prostitute something is to take that which has a proper use and to turn it into an improper use. A prostitute takes sex, which has a proper use, and perverts it with an improper use, turning it into something illicit, causing fornication. In this case, the harlot represents religion, which has a proper use (Jas. Jas. 1:26-27), but here has been prostituted for improper use. Rather than serving, it rules. The false use of religion causes spiritual fornication. The word fornication is used both of physical unfaithfulness and also of spiritual unfaithfulness, as in Hosea Hos. 1:1-Hos. 2:1; Jeremiah Jer. 2:20; Jer. 3:1-9; Ezekiel Eze. 16:15-41; Eze. 23:5-44, etc. It is with this woman that the kings of the earth commit fornication (Rev. Rev. 17:2+), showing this to be a unity of religion and state.2This aspect of the Harlot is identical with that of the city Babylon: She has made all nations drink of the wine of the wrath of her fornication (Rev. Rev. 14:8+); Those who fornicated with her were also deceived by her sorcery (Rev. Rev. 18:23+). Some believe she differs from Babylon itself, but we believe the Scriptural evidence points in the direction of identity. The woman is that great city which reigns over the kings of the earth (Rev. Rev. 17:18+)Babylon. See One or Two Babylons? Like Tyre of Isaiahs day, the Harlot has both commercial and spiritual aspects which are opposed to God: And it shall be, at the end of seventy years, that the LORD will visit Tyre. She will return to her hire, and commit fornication with all the kingdoms of the world on the face of the earth (Isa. Isa. 23:17).
and the inhabitants of the earth
As went the leaders, so went the people. Not only kings, but an entire global populace was influenced by her. Although she influenced the inhabitants throughout history, it is the earth dwellers of the time of the end which are her final drinking partners. See Earth Dwellers.
made drunk with the wine of her fornication
They were made drunk from the wine she served up (Rev. Rev. 14:8+). Because neither she nor the inhabitants of the earth chose to respond to the light which all men are given concerning God (Rom. Rom. 1:18-21), God used her rebellion to make all the nations commit even further to their errant path. Babylon was a golden cup in the LORDS hand, That made all the earth drunk. The nations drank her wine; Therefore the nations are deranged (Jer. Jer. 51:7). In the same way that the three unclean spirits go forth to draw the kings of the earth to Gods supper (Rev. Rev. 16:13-14+ cf. Rev. Rev. 19:17+), so too Babylon was a golden cup in the LORDs hand. It was her who first made them drunk, but in their consistent rejection of God and their drunken stupor they returned for more which God allowed her to continue serving up.
1 Frederick William Danker and Walter Bauer, A Greek-English Lexicon of the New Testament and Other Early Christian Literature (Chicago, IL: Uersity of Chicago Press, 2000), 693.