Genesis 14: 18: And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.
Melchizedek was God in theophany form.
Salem was the ancient name for Jerusalem.
Jerusalem was a Gentile city (it was originally inhabited by the Jebusites) in Genesis 14.
Melchizedek was King of a Gentile city in Genesis, just as Christ is King of Gentile New Jerusalem (the Bride of Christ) in Revelation 21.