John Wesley on Revelation 9:2

And there arose a smoke out of the pit - The locusts, who afterwards rise out of it, seem to be, as we shall afterwards see, the Persians; agreeable to which, this smoke is their detestable idolatrous doctrine, and false zeal for it, which now broke out in an uncommon paroxysm. As the smoke of a great furnace - where the clouds of it rise thicker and thicker, spread far and wide, and press one upon another, so that the darkness increases continually. And the sun and the air were darkened - A figurative expression, denoting heavy affliction. This smoke occasioned more and more such darkness over the Jews in Persia.