I’m literally so tired right now I can’t remember if this is true or just something some believe, or where it comes from
You are probably thinking of premillenialism, which is a fairly common belief among Protestant denominations (particularly evangelical ones), but not a universal one. Catholic and Orthodox churches both reject it. As best I can tell it’s fundamentally a Christian descendant of the Jewish messianic teachings, which are pretty weakly supported textually but tend to imply a messiah as temporal ruler; since Christianity already has its messiah, this in turn implies a second coming well before the final judgment and the destruction of the world. Eschatology in general tends to be pretty varied and speculative as theology goes, though.
You are probably thinking of premillenialism, which is a fairly common belief among Protestant denominations (particularly evangelical ones), but not a universal one. Catholic and Orthodox churches both reject it. As best I can tell it’s fundamentally a Christian descendant of the Jewish messianic teachings, which are pretty weakly supported textually but tend to imply a messiah as temporal ruler; since Christianity already has its messiah, this in turn implies a second coming well before the final judgment and the destruction of the world. Eschatology in general tends to be pretty varied and speculative as theology goes, though.