Rev 9 explains the results of fifth and sixth angels sounding their trumpets, namely the first and second "woe" referred to at the end of chapter eight. The first involves the opening of the Abyss, from which an intense smoke arose and covered the sky and contained locusts appearing like horses prepared for battle. The locusts will have tails that sting like scorpions and the power to torment and torture people who did not have the seal of God. Then when the sixth angel sounds its trumpet, there will be voice saying "release the four angels who are bound at the great river Euphrates". When they are released, they will kill 1/3 of remaining mankind with plagues from their mouths: fire, smoke, and sulfur. John concludes by explaining that the hearts of the still remaining mankind will continue to be unyielding and will even yet not repent. ( Didn't they read Exodus?)