A.T. Robertson Commentary Revelation 18:9

"And the kings of the earth, who committed fornication and lived wantonly with her, shall weep and wail over her, when they look upon the smoke of her burning," — Revelation 18:9 (ASV)

Shall weep (κλαυσουσιν). Future active of κλαιω, middle κλαυσοντα in Attic, as in Joh 16:20.

And wail over her (κα κοψοντα επ' αυτην). Future direct middle of κοπτω, old verb, to beat, to cut, middle to beat oneself (Revelation 1:7). For combination with κλαιω as here see Lu 8:52. See 17:2; 18:3,7 for ο πορνευσαντες κα στρηνιασαντες).

When they look upon (οταν βλεπωσιν). Indefinite temporal clause with οταν and the present active subjunctive of βλεπω.

The smoke of her burning (τον καπνον της πυρωσεως αυτης). Πυρωσις is an old word (from πυροω to burn), in N.T. only 1 Peter 4:12; Revelation 18:9,18. See verse 8 for other plagues on Rome, but fire seems to be the worst (17:16; 18:8,9,17; 19:3).