It's from 1 Thes. 5, NOT from the Revelation as another anon claimed.
At any rate, it is referring to APOSTATES saying, "peace, peace", just as the old false prophets used to tell unrepentant sinners, who were idolaters and burning incense to the queen of heaven, that God was at peace with them just to get favors from them. But those prophets were proven false because instead of having peace, God sent foreign nations against them, and the Jews ended up in captivity to Babylon. That's why Paul spoke about it, because he knew about the future BABYLON, the apostasy. It's something he again mentioned in 2 Thes. 2, also saying how he had spoken to them about this previously.
Bottom line, the "peace, peace" thing is in the context of apostates telling idolaters they're ok with God and blessed, just to gain favors from them. It has utterly nothing to do with world peace (though I don't believe that will ever happen, and if it were to happen, it would be temporary).