To answer the question about how the seven kings in Revelation 17 can be understood in the context of the book of Revelation being written in the year 68/69 CE I post here an extract from Thomas B. Slater. I have inserted the quotes from Revelation.
. . . John believed that the prophecies would come true soon: “And he said to me, ‘Do not seal the words of the prophecy of this book, for the time is near’” (22,10; cf. 1,1-3). . . . [W]hen John says that the events will occur soon, he refers to his book as one of prophecy. John sincerely believes that his work provides a vision of coming events. For this reason, there is no extended ex eventu prophecy, but there is some and it is found in Rev 17,9-11.
This calls for a mind with wisdom. The seven heads are seven hills on which the woman sits. They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for only a little while. The beast who once was, and now is not, is an eighth king. He belongs to the seven and is going to his destruction.
The reference to Nero as the fifth emperor is ex eventu prophecy in that it speaks of Nero’s death after the fact and predicts that he will return, an appropriation of the Nero redivivus myth. It is a stretch to argue that the Nero redivivus myth preceded Nero’s death. Thus, the Apocalypse does indeed contain ex eventu prophecy. It is quite possible that John wrote during the reign of Galba, but it is also possible that he wrote during the reign of Otho who “must only rule briefly” (17,10). To this point, John’s prophecies are historically accurate. They are inaccurate with the next ruler, Vitellius, who in no way reminded people of Nero. According to the rules of ex eventu prophecies, the book should be dated at the point where the prophecies are not fulfilled. It is possible that John was writing in 69 late in Otho’s reign or early in Vitellius’ reign.
I am, therefore, in general agreement with a date between 68-70 CE and would add one more additional bit of internal evidence. There are two examples, found in Rev 2,9 and 3,9, which have been overlooked.
I know your afflictions and your poverty—yet you are rich! I know about the slander of those who say they are Jews and are not, but are a synagogue of Satan.
I will make those who are of the synagogue of Satan, who claim to be Jews though they are not, but are liars—I will make them come and fall down at your feet and acknowledge that I have loved you.
In both passages, “Jew” is an honorific term, the religious ideal. This means that John sees himself first and foremost as a faithful Jew and that he sees the Christian community as the true Israel. His opponents are not criticized because they are Jews but because they are not faithful, righteous Jews. Such a self-identification by a Christian is more understandable in the 60’s than in the 90’s when Christians and Jews were beginning to see themselves more as separate groups. I am aware that the separation of Christianity from Judaism was a gradual, regional event that occurred at different times and different places throughout the Roman Empire; however, it is more likely that one in the Christian movement would see himself as a Jew during Nero’s reign than during Domitian’s.
An earlier date would also help to explain why the book is so Jewish and also why some exegetes have postulated that chapters 1, 2, 21 and 22 constitute a Jewish apocalypse; chapters 3-20, a Christian one. It is both Christian and Jewish at a point in time when this fact would have been a given for the original readers. Such a self-designation and self-understanding is much more intelligible in the 60’s, when Christianity was still very much within the Jewish religious community, than the 90’s, when Christianity saw itself more and more as separate and distinct from Judaism.
(Slater, 2003, pp 257-58. Bolded highlighting is mine)
— Slater, Thomas B. “Dating the Apocalypse to John.” Biblica 84, no. 2 (2003): 252–58.
Fifteen years later Slater “revisited” the above article with…
— Slater, Thomas B. “Dating the Apocalypse to John, Revisited.” Review & Expositor 114, no. 2 (May 2017): 247–53.
Quoting from that later article…
Wilson also emphasizes internal evidence and includes Galba, Otho, and Vitellius in reckoning the list of emperors. He concurs with Bell and Rowland that it is most important that Nero is clearly the fifth emperor. Wilson identifies 666 as a gematria for NERON KAISAR. “When the name is put into Hebrew and the numerical equivalents of the Hebrew letters are added together, the sum is 666.” In addition, he provides the most credible explanation for the “616” variant reading in some manuscripts. “The 616 (variant) would take the final nun off the name Neron in order to render it Nero, the acceptable way of saying the name in Greek.” Because Nero is the fifth emperor, Galba is the sixth, “the one who is,” and Otho is yet to come. For Wilson, as for Bell and Rowland, the Apocalypse dates to the reign of Galba. Although I agree in general, elsewhere I have argued that John wrote Revelation during the reign of Vitellius, but I would not lose sleep if it were proven to have been written during Galba’s reign.
I am, therefore, in general agreement with a date between 68–70 CE, and would offer additional evidence. First are two examples, found in Rev 2:9 (“those who say they are Jews [though they are not but are really Satan’s synagogue]” and similarly in 3:9), which have been overlooked. In both passages, being Jewish is the religious ideal. John did not castigate his opponents because they were Jews but because they were not faithful Jews. Such a self-understanding is more conceivable in the 60s than the 90s.
Another factor overlooked in dating the book is John’s position on eating meat offered to idols in Rev 2:14 and 2:20, a position diametrically opposed to Paul’s more moderate position in 1 Corinthians 8. John sees Paul’s position as an unfaithful accommodation, if not capitulation, to social norms and expectations. It is highly unlikely that a Christian leader would consciously and openly oppose Paul during the 90s in the same area in which Paul had an extensive presence and where Christians from all theological perspectives would have collected Paul’s letters, regularly quoting them as authoritative. Indeed, everyone wants to be the acknowledged successor to Paul the Apostle in the 90s. We know, however, from Paul’s own letters of his ardent opponents in the 50s and 60s (e.g., Gal 1:10–2:10; 2 Cor 11:1–33).
Another internal factor is the accusation of false apostles in Rev 2:2: “You have tested those who say they are apostles but are not, and you have found them to be liars.” By the 90s there was no longer any debate who the apostles were. Again, the argument was who faithfully followed the teachings and practices of the apostles. Such an assertion about false apostles would be more likely and necessary during the 60s than the 90s.20 Moreover, above I noted that John intentionally opposed Paul in the same region.
(Slater, 2017, 251-252)
Note that this post is part of a larger series in which I will present a case for dating Revelation to the second century.